A Dictionary of Units New One

8/4/2019 A Dictionary of Units New One

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A Dictionary of Units

Summary table of conversion factors most often required

x means 'multiply by' . . . / means 'divide by' . . . # means it is an exact value

All other values given to an appropriate degree of accuracy.

To change . . into . . do this . . To change . . into . . do this . .

acres hectares x 0.4047 kilograms ounces x 35.3

acres sq. kilometres / 247 kilograms pounds x 2.2046

acres sq. metres x 4047 kilograms tonnes / 1000 #

acres sq. miles / 640 # kilograms tons (UK/long) / 1016

barrels (oil) cu.metres / 6.29 kilograms tons (US/short) / 907

barrels (oil) gallons (UK) x 34.97 kilometres metres x 1000 #

barrels (oil) gallons (US) x 42 # kilometres miles x 0.6214

barrels (oil) litres x 159 litres cu.inches x 61.02

centimetres feet / 30.48 # litres gallons (UK) x 0.2200

centimetres inches / 2.54 # litres gallons (US) x 0.2642

centimetres metres / 100 # litres pints (UK) x 1.760

centimetres millimetres x 10 # litres pints (US liquid) x 2.113

cubic cm cubic inches x 0.06102 metres yards / 0.9144 #

cubic cm litres / 1000 # metres centimetres x 100 #

cubic cm millilitres x 1 # miles kilometres x 1.609

cubic feet cubic inches x 1728 # millimetres inches / 25.4 #

cubic feet cubic metres x 0.0283 ounces grams x 28.35

cubic feet cubic yards / 27 # pints (UK) litres x 0.5683

cubic feet gallons (UK) x 6.229 pints (UK) pints (US liquid) x 1.201

cubic feet gallons (US) x 7.481 pints (US liquid) litres x 0.4732

cubic feet litres x 28.32 pints (US liquid) pints (UK) x 0.8327

cubic inches cubic cm x 16.39 pounds kilograms x 0.4536

cubic inches litres x 0.01639 pounds ounces x 16 #

cubic metres cubic feet x 35.31

To change . . into . . do this . . To change . . into . . do this . .

square cm sq. inches x 0.1550

feet centimetres x 30.48 # square feet sq. inches x 144 #

feet metres x 0.3048 # square feet sq. metres x 0.0929

feet yards / 3 # square inches square cm x 6.4516 #

fl.ounces (UK) fl.ounces (US) x 0.961 square inches square feet / 144 #

fl.ounces (UK) millilitres x 28.41 square km acres x 247

fl.ounces (US) fl.ounces (UK) x 1.041 square km hectares x 100 #fl.ounces (US) millilitres x 29.57 square km square miles x 0.3861

gallons pints x 8 # square metres acres / 4047

gallons (UK) cubic feet x 0.1605 square metres hectares / 10 000 #

gallons (UK) gallons (US) x 1.2009 square metres x 10.76

gallons (UK) litres x 4.54609 # square metres square yards x 1.196

gallons (US) cubic feet x 0.1337 square miles acres x 640 #

gallons (US) gallons (UK) x 0.8327 square miles hectares x 259

gallons (US) litres x 3.785 square miles square km x 2.590

grams kilograms / 1000 # square yards square metres / 1.196

grams ounces / 28.35 tonnes kilograms x 1000 #

hectares acres x 2.471 tonnes tons (UK/long) x 0.9842

hectares square km / 100 # tonnes tons (US/short) x 1.1023

hectares square metres x 10000 # tons (UK/long) kilograms x 1016hectares square miles / 259 tons (UK/long) tonnes x 1.016

hectares square yards x 11 960 tons (US/short) kilograms x 907.2

inches centimetres x 2.54 # tons (US/short) tonnes x 0.9072

inches feet / 12 # yards metres x 0.9144 #

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Categories of Units

length

area

volume or capacity

mass

temperature

density, area

density, line

density, volume

energy

force

power

pressure

speed

spread rate (by mass)

spread rate (by volume)


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fuel consumption

mass per unit length

mass per unit area

mass per unit volume

stress

torque

Length

The S I unit of length is the metre. To change a ny of these other units of length into their equivalent values in metres use the operation and

conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy. Where some uncertainty is

indicated it means that a good idea of the size of the unit can be given but that a better value would depend upon knowing th e period and/or

culture in which the unit was being used.

Note than in matters concerned with land measurements, for the mos t accurate work, it is necessary to establish whether the US survey m easures

are being used or not.

angstroms divide by 10 000 000 000 #

astronomical units x 149 598 550 000

barleycorns x 0.008 467

centimetres x 0.01 #

chains (surveyors') x 20.1168 #

cubits x (0.45 to 0.5)

ells (UK) x 0.875 (but many variations)

ems (pica) x 0.004 233 3

fathoms x 1.8288 #

feet (UK and US) x 0.3048 #

feet (US survey) x 0.304 800 609 6

furlongs x 201.168 #

hands x 0.1016 #inches x 0.0254 #

kilometres x 1000 #

leagues x (4000 to 5000)

light years x 9 460 500 000 000 000

links (surveyors') x 0.201 168 #

metres [m] 1

microns (=micrometres) x 0.000 001 #

miles (UK and US) x 1609.344 #

miles (nautical) x 1852 #

parsecs x 30 856 770 000 000 000

perch (=rods or poles) x 5.0292 #

picas (computer) x 0.004 233 333

picas (printers') x 0.004 217 518

points (computer) x 0.000 352 777 8

points (printers') x 0.000 351 459 8

yards x 0.9144 #

Area

The S I unit of area is the square metre. To change any of these other units of area into their equivalent values in square metres use the operation

and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy. Where some uncertainty

is indicated it means that a good idea of the size of the unit can be given but that a better value would depend upon knowing the period and/or

culture in which the unit was being used. Note than in matters concerned with land measurements, for the most accurate work, it is necessary to

establish whether the US survey measures are being used or not.

acres x 4046.856 422 4 #

ares x 100 #

circular inches x 0.000 506 707 479hectares x 10 000 #

hides x 485 000 (with wide variations)

roods x 1011.714 105 6 #

square centimetres x 0.000 1 #

square feet (UK and US) x 0.092 903 04 #

square feet (US survey) x 0.092 903 411 613

square inches x 0.000 645 16 #

square kilometres x 1 000 000 #

square metres 1

square miles x 2 589 988.110 336 #

square millimetres x 0.000 001 #

squares (of timber) x 9.290 304 #


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square rods (or poles) x 25.292 852 64 #

square yards x 0.836 127 36 #

townships x 93 239 571.972

Volume or Capacity

The S I unit of volume is the cubic metre. However, this seems to be much less used than the litre (1000 litres = 1 cubic metre).To change any of

these other units of volume into their equivalent values in litres use the operation and conversion factor given. Those marked with #

are exact. Other values are given to an appropriate degree of accuracy.

The litre. There can be some ambiguity about the size of the litre. When the metric system was introduced in the 1790's the litre was in tended to

match up with the volume occupied by 1 kilogram of pure water at a specified pressure and temperature. As the ability to measure things got

better (by 100 years later) they found that there was a mismatch between the kilogram and the litre. As a result of this they had to redefine the

litre (in 1901) as being 1 .000028 cubic decimetres. Very handy!

This nonsense was stopped in 1964 when it was ruled that the word "litre" may be employed as a special name for the cubic decimetre, with the

additional recommendation that for really accurate work, to avoid any possible confusion, the litre should not be used.

Here the litre is taken as being a cubic decimetre.

barrels (oil) x 158.987 294 928 #

bushels (UK) x 36.368 72 #

bushels (US) x 35.239 070 166 88 #

centilitres x 0.01 #

cubic centimetres x 0.001 #

cubic decimetres 1

cubic decametres x 1 000 000 #

cubic feet x 28.316 846 592 #

cubic inches x 0.016 387 064 #

cubic metres x 1000 #

cubic millimetres x 0.000 001 #

cubic yards x 764.554 857 984 #

decilitres x 0.1 #

fluid ounces (UK) x 0.028 413 062 5 #

fluid ounces (US) x 0.029 573 529 562 5 #

gallons (UK) x 4.546 09 #

gallons, dry (US) x 4.404 883 770 86 #

gallons, liquid (US) x 3.785 411 784 #

litres [l or L] 1

litres (1901 - 1964) x 1.000 028

millilitres x 0.001 #

pints (UK) x 0.568 261 25 #pints, dry (US) x 0.550 610 471 357 5 #

pints, liquid (US) x 0.473 176 473 #

quarts (UK) x 1.136 522 5 #

quarts, dry (US) x 1.101 220 942 715 #

quarts, liquid (US) x 0.946 352 946 #

Mass (or Weight)

The S I unit of mass is t he kilogram. To change any of these other units of mass into their equivalent values in kilograms use the operation and

conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.

carats, metric x 0.000 2 #

grains x 0.000 064 798 91 #

grams x 0.001 #

hundredweights, long x 50.802 345 44 #

hundredweights, short x 45.359 237 #

kilograms [kg] 1

ounces, avoirdupois x 0.028 349 523 125 #

ounces, troy x 0.031 103 476 8 #

pounds x 0.453 592 37 #

slugs (or g-pounds) x 14.593 903

stones x 6.350 293 18 #

tons (UK or long) x 1016.046 908 8 #

tons (US or short) x 907.184 74 #

tonnes x 1000 #

Temperature


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There have been five ma in temperature scales, each one being named after the person who invented it.

G D FAHRENH EIT (1686-1736) a German physicist, in about 1714 proposed the first practical scale. He called the freezing-point of water 32 degrees

(so as to avoid negative temperatures) and the boiling -point 212 degrees.

R A F de REAUMUR (1673-1757) A French entomologist, proposed a similar scale in 1730, but set the freezing -point at 0 degrees and the boiling-

point at 80 degrees. This was used quite a bit but is now obsolete.

Anders CELSIUS (1701-1744) a Swedish astronomer, proposed the 100 -degree scale (from 0 to 100) in 1742. This was widely adopted as the

centigrade scale. But since grades and centigrades were also measures of angle, in 1947 it officially became the Celsius scale. Also, the S I system of

units gives preference to naming units after people where possible.

William Thomson, 1st Lord KELVIN (1824 -1907) a Scottish mathema tician and physicist, worked with J P Joule - about 1862 - to produce an

absolute scale of temperature based on laws of heat rather than the freezing/boiling -points of water. This work produced the idea of 'absolute

zero', a temperature below which it was not possible to go. Its value is -273.15 degrees on the Celsius scale.

William J M RANKINE (1820 -1872) a Scottish engineer and scientist, promoted the Kelvin scale in its Fahrenheit form, when the equivalent value of

absolute zero is -459.67 degrees Fahrenheit.

Nowadays, while scientists use the KELVIN scale, the CELSIUS scale is the preferred scale in our everyday lives. However, the Fahrenheit scale is still

widely used and there frequently is a need to be able to chan ge from one to the other.

To change temperature given in Fahrenheit (F) to Celsius (C)

Start with (F); subtract 32; multiply by 5; divide by 9; the answer is ( C)

To change temperature given in Celsius ( C) to Fahrenheit (F)

Start with (C); multiply by 9; divide by 5; add on 32; the answer is (F)

Line density

Line density is a measure of mass per unit length. The S I compatible unit of line density is kilograms/metre . A major use of line density is in the

textile industry to indicate the coarseness of a yarn or fibre. For that purpose the SI unit is rather large so the preferred unit there is the tex. (1 tex

= 1 gram/kilometre) To change a ny of these other units of line density into their equivalent values in kilograms/metre use the operation andconversion factor given. Those marked with # are exact.Other values are given to an appropriate degree of a ccuracy.

denier divide by 9 000 000 #

drex divide by 10 000 000 #

grams/centimetre divide by 10 #

grams/kilometre (tex) divide by 1 000 000 #

grams/metre divide by 1000 #

grams/millimetre 1

kilograms/kilometre divide by 1000 #

kilograms/metre 1

milligrams/centimetre divide by 10 000 #

milligrams/millimetre divide by 1000 #

ounces/inch x 1.116 125ounces/foot x 0.093 01

pounds/inch x 17.858

pounds/foot x 1.488 164

pounds/yard x 0.496 055

pounds/mile x 0.000 281 849

tex divide by 1 000 000 #

tons(UK)/mile x 0.631 342

tons(US)/mile x 0.563 698

tonnes/kilometre 1

Density

Density is the shortened term generally used in place of the more accurate des cription volumetric density.It is a measure of mass per unit volume.

The S I compatible unit of density is kilograms/cubic metre. However, this a rather large unit for most purposes (iron is over 7000, wood is about

600 and even cork is over 200). A much m ore useful size of unit is kilograms/litre (for which the previous values then become 7, 0 .6 and 0.2

respectively). This unit also has the great advantage of being numerically unchanged for grams/cubic centimetre and tonnes/cu bic metre (or

megagrams/cubic metre). To change any of these other units of density into their equivalent values in kilograms/litre use the operation and


grains/gallon(UK) divide by 70 157

grains/gallon(US) divide by 58 418

grams/cubic centimetre 1

grams/litre divide by 1000 #

grams/millilitre 1

kilograms/cubic metre divide by 1000 #

megagrams/cubic metre 1

milligrams/millilitre divide by 1000 #

milligrams/litre divide by 1 000 000 #


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kilograms/litre 1

ounces/cubic inch x 1.729 994 044

ounces/gallon(UK) x 0.006 236 023

ounces/gallon(US) x 0.007 489 152

pounds/cubic inch x 27.679 905

pounds/cubic foot x 0.016 018 463

pounds/gallon(UK) x 0.099 776 373

pounds/gallon(US) x 0.119 826 427

tonnes/cubic metre 1

tons(UK)/cubic yard x 1.328 939 184

tons(US)/cubic yard x 1.186 552 843

Energy or work

There is a lot of room for confusion in some of the units used here. The calorie can take 5 different values and, while these do not vary by very

much, for accurate work it is necessary to specify which calorie is being used.

The 5 calories are known as the

International Table calorie = cal(IT)

thermochemical calorie = cal(th)

mean calorie = cal(mean)

15 degree C calorie = cal(15C)

20 degree C calorie = cal(20C).

Unless a clear statement is made saying otherwise, assume the IT calorie is being used.

As a further complication, in working with food and expressing nutritional values, the unit of a Calorie (capital C) is often used to represent 1000

calories, and again it is necessary to specify which calorie is being used for that.

The British thermal unit (Btu) can also take different values and they are named in a similar way to the calorie, that is Btu (IT), (th), etc. Also note

that the therm is100 000 Btu so its exact size depends on which Bt u is being used.

The S I unit of energy or w ork is the joule. To change any of these other units of energy or work into their equivalent values in joules use the

operation and conversion factor given. Those marked with # a re exact. Other values are given to an appropriate degree of accuracy.

British thermal units(IT)x 1055.056

Btu (th) x 1054.350

Btu (mean) x 1055.87

calories - cal (IT) x 4.1868 #

- cal (th) x 4.184 #

- cal (mean) x 4.190 02

- cal (15C) x 4.185 80

- cal (20C) x 4.181 90

Calorie (food) x 4186 (approx.)

centigrade heat units x 1900.4

ergs divide by 10 000 000 #foot pounds-force x 1.355 818

foot poundals x 0.042 140

gigajoules [GJ] x 1000 000 000 #

horsepower hours x 2 684 520 (approx.)

joules [J] 1

kilocalories (IT) x 4186.8 #

kilocalories (th) x 4184 #

kilogram-force metres x 9.806 65 #

kilojoules [kJ] x 1000 #

kilowatt hours [kWh] x 3 600 000 #

megajoules [MJ] x 1 000 000 #

newton metres [Nm] x 1 #

therms x 105 500 000 (approx.)

watt seconds [Ws] 1

watt hours [Wh] x 3600 #

Force

The S I unit of force is the newton. To change any of these other units of force into their equivalent values in newtons use the operation and


dynes divide by 100 000 #

kilograms force x 9.806 65 #

kilonewtons [kN] x 1000 #

kips x 4448.222

meganewtons [MN] x 1 000 000 #


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newtons [N] 1

pounds force x 4.448 222

poundals x 0.138 255

sthenes (=kN) x 1000

tonnes force x 9806.65 #

tons(UK) force x 9964.016

tons(US) force x 8896.443

Fuel Consumption

Fuel consumption of any means of transport (car, aeroplane, ship etc.) that uses fuel is a measure giving the relationship be tween the distance

travelled for an amount of fuel used. The most common example is the car where it is usually express ed (in English-speaking countries) in miles per

gallon.

It could also be expressed in gallons per mile. However, for a car the latter method gives a rather small figure: 35 miles pe r gallon is about 0.0286

gallons per mile. In that case it would be better to give a figure for 100 miles, so it would be 2.86 gallons per 100 miles. That is the metric way of

expressing fuel consumption - as litres per 100 kilometres.

From regular enquiries it appears that in real life people are using all sorts of ways of exp ressing their fuel consumption, so this section (unlike all

the others) tries to cover as many wa ys as possible. All the values are given to an accuracy of 4 significant figures.

To change into

miles per gallon (UK) miles per gallon (US) multiply by 0. 833

miles per gallon (UK) miles per litre multiply by 0.22

miles per litre miles per gallon (UK) multiply by 4.546

miles per gallon (UK) kilometres per litre multiply by 0.354

miles per gallon (US) miles per gallon (UK) multiply by 1.2

miles per gallon (US) miles per litre multiply by 0.2642

miles per litre miles per gallon (US) multiply by 3.785

miles per gallon (US) kilometres per litre multiply by 0.4251

Xmiles per gallon gallons per 100 miles: divide 100 by X

(both gallons must of the same type)

Xmiles per gallon (UK) litres per 100 km: divide 282.5 by X

Xmiles per gallon (US) litres per 100 km: divide 235.2 by X

Xkm per litre litres per 100 km: divide 100 by X

Xmiles per litre litres per 100 km: divide 62.14 by X

Power

Since power is a measure of the rate at which work is done, the underlying units are those of work or energy, and that section should be looked at

for explanations concerning the calorie and Btu. In this section the (IT) values have been used.

In this section it is the horsepower which provides confusion. Just like the calorie, it can take 5 different values, and these are identified as

necessary by the ad dition of (boiler), (electric), (metric), (UK) and (water). Unlike the calorie (whose 5 values are reasonably close to each other) ,

the horsepower has 4 which are close and 1 (boiler) which is considerably different - it is about 13 times bigger than the others - but it seems to be

very little used.

The S I unit of power is the watt. To change any of these other units of energy or work into their equivalent values in watts use the operation and


Btu/hour x 0.293 071

Btu/minute x 17.584 267

Btu/second x 1055.056

calories/hour x 0.001 163 #

calories/minute x 0.069 78 #

calories/second x 4.1868 #

ft lb-force/minute x 0.022 597

ft lb-force/second x 1.355 82gigawatts [GW] x 1 000 000 000

horsepower (electric) x 746 #

horsepower (metric) x 735.499

watts [W] 1

joules/hour divide by 3600 #

joules/minute divide by 60 #

joules/second 1

kilocalories/hour x 1.163

kilocalories/minute x 69 .78

kg-force metres/hour x 0.002 724

kg-force metres/minute x 0.163 444


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kilowatts [kW] x 1000 #

megawatts [MW] x 1 000 000 #

Pressure or Stress

The S I unit of pressure is the pascal. The units of pressure are defined in the same way as those for stress - force/unit area. To change any of these

other units of pressure (or stress) into their equivalent values in pascals use the operation and conversion factor given. Those marked with #

are exact. Other values are given to an appropriate degree of accuracy. M easures based on water assume a density of 1 kg/litre - a value which is

rarely matched in the real world, though the error is small.

atmospheres x 101 325 #

bars x 100 000 #

centimetres of mercury x 1333.22

centimetres of water x 98.066 5 #

feet of water x 2989.066 92 #

hectopascals [hPa] x 100 #

inches of water x 249.088 91 #

inches of mercury x 3386.388

kg-force/sq.centimetre x 98 066.5 #

kg-force/sq.metre x 9.806 65 #

kilonewton/sq.metre x 1000 #

kilopascal [kPa] x 1000 #

kips/sq.inch x 6 894 760

meganewtons/sq.metre x 1 000 000 #

metres of water x 9806.65 #

millibars x 100 #

pascals [Pa] 1

millimetres of mercury x 133.322

millimetres of water x 9.806 65 #

newtons/sq.centimetre x 10 000

newtons/sq.metre 1

newtons/sq.millimetre x 1 000 000 #

pounds-force/sq.foot x 47.880

pounds-force/sq.inch x 6894.757

poundals/sq.foot x 1.448 16

tons(UK)-force/sq.foot x 107 252

tons(UK)-force/sq.inch x 15 444 256

tons(US)-force/sq.foot x 95 760

tons(US)-force/sq.inch x 13 789 500

tonnes-force/sq.cm x 98 066 500 #tonnes-force/sq.metre x 9806.65 #

Speed

The S I compatible unit of speed is metres/second. To change any of these other units of speed into their equivalent values in metres/second use

the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accuracy.

centimetres/minute divide by 6000 #

centimetres/second divide by 100 #

feet/hour divide by 11 811

feet/minute x 0.005 08 #

feet/second x 0.3048 #

inches/minute divide by 2362.2

inches/second x 0.0254 #

kilometres/hour divide by 3.6 #

kilometres/second x 1000 #knots x 0.514 444

Mach number x 331.5

metres/hour divide by 3600 #

metres/minute divide by 60 #

metres/second [m/s] 1

miles/hour x 0.447 04 #

miles/minute x 26.8224 #

miles/second x 1609.344 #

yards/hour divide by 3937

yards/minute x 0.015 24 #

yards/second x 0.9144 #


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Spread Rate (by mass)

The spread rate of a substance is a measure of how much of it there is covering a unit area. The 'how much' can be measure d by volume or by

mass. The S I compatible unit of spread rate by mass is kilograms/square metre . It is also a measure of area density (mass/unit area) and is similar

to - but not the same as - pressure, which is force/unit area. For the rainfall conversions a density of 1 kg/litre has been assumed. To change any of

these other units of spread rate into their equivalent values in kilograms/square metre use the operation and conversion factor given. Those

marked with # are exact. Other values are given to an appropriate degree of accuracy. The conversion for rainfall assumes a density of 1 kg/ litre

which is accurate enough for all practical purposes.

grams/sq.centimetre x 10 #

grams/sq.metre divide by 1000 #

inches of rainfall x 2.54

kilograms/hectare divide by 10 000 #kilograms/sq.centimetre x 10 000 #

milligrams/sq.metre divide by 1000 #

millimetres of rainfall 1

kilograms/sq.metre 1

ounces/sq.foot x 0.305 152

ounces/sq.inch x 43.942

ounces/sq.yard divide by 49.494

pounds/acre divide by 8921.791

pounds/sq.foot x 4.882 428

pounds/sq.inch x 703.07

pounds/sq.yard x 0.542 492

tonnes/hectare divide by 10 #

tons(UK)/acre divide by 3.982 942tons(US)/acre divide by 4.460 896

Spread Rate (by volume)

The spread rate of a substance is a measure of how much of it there is covering a unit area. The 'how much' can be measured by volume or by

mass. The S I compatible unit of spread rate by volume is cubic metres/square metre . However, this is a rather large unit for most purposes and so

litres/square metre is often preferred. To change any of these other units of spread rate into their equivalent values in litres/square metre use the

operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of accur acy.

cubic feet/acre divide by 142.913

cubic inches/sq.yard divide by 51.024

cubic yards/sq.mile divide by 3387.577

cubic metres/hectare divide by 10 #

cubic metres/sq.km divide by 1000 #

cubic metres/sq.metre x 1000 #fl. ounces(UK)/sq.yard divide by 29.428

litres/square metre 1

gallons(UK)/acre divide by 890.184

gallons(US)/acre divide by 1069.066

gallons(UK)/hectare divide by 2199.692

gallons(US)/hectare divide by 2641.721

inches of rainfall x 25.4 #

litres/hectare divide by 10 000 #

millilitres/sq.metre divide by 1000 #

millimetres of rainfall 1

Torque

The S I compatible unit of torque is the newton metre. To change any of these other units of torque into their equivalent values in newton

metres use the operation and conversion factor given. Those marked with # are exact. Other values are given to an appropriate degree of

accuracy.

dyne centimetres divide by 10 000 000 #

gram-force centimetres x 0.000 098 066 5 #

kg-force centimetres x 0.098 066 5 #

kg-force metres x 9.806 65 #

newton centimetres divide by 100 #

newton metres [Nm] 1

ounce-force inches divide by 141.612

pound-force inches x 0.112 984


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pound-force feet x 1.355 818

poundal feet x 0.042 140

ton(UK)-force feet x 3 037.032

ton(US)-force feet x 2 711.636

tonne-force metres x 9 806.65 #

Notes

Errors

Whilst every care has been taken in the compilation of this document,

and many checks have been carried out, the possibility of an error is

always present in a work like this and that must be borne in mind by

all users. The author would be glad to be told of any errors detected.

Accuracy

In a general dictionary like this it is impossible to know just what

accuracy is needed by any particular user. Where the given value is

an exact one then it has been signalled. In most cases other values are

accurate to at least the n umber of significant figures shown. In some

cases it might be more than that as trailing zeros have not been

included.

Presentation

The conversion factors have mainly been presented as multipliers, but

exceptions to that have been made for two reasons. First, it is easier

to convey the exact value 'divide by 60' rather than the approximation

'multiply by 0 .0166667' and it is more likely to be keyed in without

errors if a calculator is being used. Second, most calc ulators accept

only 8 digits, which means that 'multiply by 0 .000 084 666' will

become '0.000 0846' (3 significant figures) whereas 'divide by 11 811'

will give the result to 6 significant figures. The appearance of a '1'

needs no operator but shows that t he named unit is exactly equivalent

to the standard unit.

Inverse usage

In nearly all cases the conversion factors have been given to change

'non-standard' units into standard units of the SI. For those cases

where it is necessary to do a conversion the o ther way it is only a

matter of reversing the operation. For example to convert feet into

metres you multiply by 0.3048 so, to convert metres into feet

you divide by 0.3048. Following on from this it can be seen how

conversions can be made between non- standard units, changing first

into the standard unit and then back into the required unit.

Author's Note

A guiding principle behind the writing and presentation of this

document has been that ofclarity for non-specialist readers. To that

end I have been guilty of breaking "the rules" in a few places. I am

sorry that these transgressions may offend some readers but I have

done so in the belief that it will be a little bit easier for many, and also

help the flow of a continuous narrative.

This dictionary is not meant to be encyclopaedic in its coverage, and

there are many many more units which are not touched upon, but it is

hoped that all 'ordinary' needs are covered. The many references to

other sources, both in books and on- line should take care of anything

beyond that.

Finally, I must thank all of those who wrote with suggestions (and

corrections!) after reading the earlier editions.

This provides a summary of most of the units of measurement to be found in use around the world today (and a few of historic al interest), and

the definitions and rules of the various systems in which they are found.

Conversions between the various units are dealt with in Part 1

There are NO units of currency.

There is an outline of the S I system,

a list of its 7 basic definitions,

some of its derived units,

together with a list of all the S I prefixes,

and some of the rules and conventions for its usage.

On the subject of measures generally, there is a short historical note.

Then there are descriptions of the Metric system,

and the U K (Imperial) system,

followed by statements on the implementation of 'metrication' in the U K,

and then the U S system of measures.

At the bottom of this document is a list of other sources,

and also some links to other Web sites.

And then there is its publishing history .

There is a separate document covering the most FAQ and other measures.

The Systeme International [S I]

Le Systeme international d'Unites officially came into being in October 1960 and has been officially recognised and adopted by nearly all countries,

though the amount of actual usage varies considerably. It is based upon 7 principal units, 1 in each of 7 different categorie s -

Category Name Abbrev.

Length metre m

Mass kilogram kg

Time second s

Electric current ampere A

Temperature kelvin K

Amount of substance mole mol

Luminous intensity candela cd

Definitions of these basic units are given. Each of these units may take a prefix. From these basic units many other units are derived and named.

Definitions of the Seven Basic S I Units


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metre [m]

The metre is the basic unit of length. It is the distance light travels, in a vacuum, in 1/ 299792458th of a second.

kilogram [kg]

The kilogram is the basic unit of mass. It is the mass of an international prototype in the form of a platinum -iridium

cylinder kept at Sevres in France. It is now the only basic unit still defined in terms of a material object, and also the only

one with a prefix[kilo] already in place.

second [s]

The second is the basic unit of time. It is the length of time taken for 9192631770 periods of vibration of th e caesium-

133 atom to occur.

ampere [A]

The ampere is the basic unit of electric current. It is that current which produces a specified force between two parallel

wires which are 1 metre apart in a vacuum. It is named after the French physicist Andre Ampere (1775-1836).kelvin [K]

The kelvin is the basic unit of temperature. It is 1/273 .16th of the thermodynamic temperature of the triple point of

water.It is named after the Scottish mathematician and physicist William Thomson 1st Lord Kelvin (1824 -1907).

mole [mol]

The mole is the basic unit of substance. It is the amount of substance that contains as many elementary units as there

are atoms in 0 .012 kg of carbon-12.

candela [cd]

The candela is the basic unit of luminous intensity. It is the intensity of a s ource of light of a specified frequency, which

gives a specified amount of power in a given direction.

Derived Units of the S I

From the 7 basic units of the SI other units are derived for a variety of purposes. Only a few of are explained here as examples, there are many

more.

farad [F]

The farad is the SI unit of the capacitance of an electrical system, that is, its capacity to store electricity. It is a rath er

large unit as defined and is more often used as a m icrofarad. It is named after the English chemist and physicist Michael

Faraday (1791-1867).

hertz [Hz]

The hertz is the SI unit of the frequency of a periodic phenomenon. One hertz indicates that 1 cycle of the phenomenon

occurs every second. For most work much higher frequencies are needed such as the kilohertz [kHz] and megahertz

[MHz]. It is named after the German physicist Heinrich Rudolph Hertz (1857- 94).

joule [J]

The joule is the SI unit of work or energy. One joule is the amount of work done when an applied forc e of

1 newton moves through a distance of 1 metre in the direction of the force. It is named after the English physicist James

Prescott Joule (1818-89).

newton [N]

The newton is the SI unit of force. One newton is the force required to give a mass of 1 kilogram an acceleration of

1 metre per second per second.It is named after the English mathematician and physicist Sir

Isaac Newton (1642 -1727).

ohm []

The ohm is the SI unit of resistance of an electrical conductor. Its symbol, is the capital Greek letter 'omega'. It is named

after the German physicist Georg Simon Ohm (1789-1854).

pascal [Pa]

The pascal is the SI unit of pressure. One pascal is the pressure generated by a force of 1 newton acting on an area of 1

square metre. It is a rather small unit as de fined and is more often used as a kilopascal [kPa]. It is named after the

French mathematician, physicist and philosopher Blaise Pascal (1623 -62).

volt [V]

The volt is the SI unit of electric potential. One volt is the difference of potential between two p oints of an electical

conductor when a current of 1 ampere flowing between those points dissipates a power of 1 watt. It is named after the

Italian physicist Count Alessandro Giuseppe Anastasio Volta (1745-1827).

watt [W]

The watt is used to measure power or the rate of doing work. One watt is a power of 1 joule per second. It is named

after the Scottish engineer James Watt (1736-1819).

Note that prefixes may be used in conjunction with any of the above units.

The Prefixes of the S I

The S I allows the sizes of units to be made bigger or smaller by the use of appropriate prefixes. For example, the electrical unit of a wat t is not a

big unit even in terms of ordinary household use, so it is generally used in terms of 1000 watts at a time. The prefix for 1000 is kilo so we use

kilowatts[kW] as our unit of measurement. For makers of electricity, or bigger users such as industry, it is common to use me gawatts[MW] or even

gigawatts[GW]. The full range of prefixes with their [symbols or abbreviations] and their multiplying factors which are also given in other forms is

yotta [Y] 1 000 000 000 000 000 000 000 000 = 10^24

zetta [Z] 1 000 000 000 000 000 000 000 = 10^21

exa [E] 1 000 000 000 000 000 000 = 10^18

peta [P] 1 000 000 000 000 000 = 10^15

tera [T] 1 000 000 000 000 = 10^12


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giga [G] 1 000 000 000 (a thousand millions = a billion)

mega [M] 1 000 000 (a million)

kilo [k] 1 000 (a thousand)

hecto [h] 100 (a hundred)

deca [da]10 (ten)

1

deci [d] 0.1 (a tenth)

centi [c] 0.01 (a hundredth)

milli [m] 0.001 (a thousandth)

micro [] 0.000 001 (a m illionth)

nano [n] 0.000 000 001 (a thousand millionth)

pico [p] 0.000 000 000 001 = 10^-12femto [f] 0.000 000 000 000 001 = 10^-15

atto [a] 0.000 000 000 000 000 001 = 10^-18

zepto [z] 0.000 000 000 000 000 000 001 = 10^-21

yocto [y] 0.000 000 000 000 000 000 000 001 = 10^-24

[] the symbol used for micro is the Greek letter known as 'mu'

Nearly all of the S I prefixes are multiples (kilo to yotta) or sub -multiples (milli to yocto) of 1000. However, these are inconvenient for many

purposes and so hecto,deca, deci, and centi are also used.

deca also appears as deka [da] or [dk] in the USA and Contintental Europe. So much for standards!

Call up a Conversion Calculator for Prefixes

OR Notes on Prefixes (inc. other types)

Conventions of Usage in the S I

There are various rules laid down for the use of the SI and its units as well as some observations to be made that will help in its correct use.

y Any unit may take only ONE prefix. For example 'millimillimetre' is incorrect and should be written as'micrometre'.

y Most prefixes which make a unit bigger are written in capital letters (M G T etc.), but when they m ake a unitsmaller then lower case (m n p etc.) is used. Exceptions to this are the kilo [k] to a void any possible confusion

with kelvin [K]; hecto [h]; and deca [da] or [dk]

y It will be noted that many units are eponymous, that is they are named after pers ons. This is always someonewho was prominent in the early work done within the field in which the unit is used. Such a unit is written all

in lower case (newton, volt, pascal etc.) when named in full, but starting with a capital letter (N V Pa etc.)

when abbreviated. An exception to this rule is the litre which, if written as a lower case 'l' could be mistaken

for a '1' (one) and so a capital 'L' is allowed as an alternative. It is intended that a single letter will be decided

upon some time in the future when it becomes clear which letter is being favoured most in use.

y Units written in abbreviated form are NEVER pluralised. So 'm' could always be either 'metre' or 'metres'. 'ms'would represent 'millisecond'.

y An abbreviation (such as J N g Pa etc.) is NEVE R followed by a full-stop unless it is the end of a sentence.y To make numbers easier to read they may be divided into groups of 3 separated by spaces (or half -spaces)

but NOT commas.

y The SI preferred way of showing a decimal fraction is to use a comma (123 ,456) to separate the wholenumber from its fractional part. The practice of using a point, as is common in English -speaking countries, is

acceptable providing only that the point is placed ON the line of the bottom edge of the numbers (123 .456)

and NOT in the m iddle.

A Brief History of Measurement

One of the earliest types of measurement concerned that of length. These measurements were usually based on parts of the body . A well

documented example (the first) is the Egyptian cubit which was derived from the length of the arm from the elbow to the outstretched finger tips.

By 2500 BC this had been standardised in a royal master cubit made of black marble (about 52 cm). This cubit was divided into 28 digits (roughly a

finger width) which could be further d ivided into fractional parts, the smallest of these being only just over a millimetre.

In England units of measurement were not properly standardised until the 13th century, though variations (and abuses) continu ed until long after

that. For example, there were three different gallons (ale, wine and corn) up until 1824 when the gallon was standardised.

In the U S A the system of weights and measured first adopted was that of the English, though a few differences came in when decisions were

made at the time of standardisation in 1836. For instance, the wine -gallon of 231 cubic inches was used instead of the English one (as defined in

1824) of about 277 cubic inches. The U S A also took as t heir standard of dry measure the old Winchester bushel of 2150 .42 cubic inches, which

gave a dry gallon of nearly 269 cubic inches.

Even as late as the middle of the 20th century there were some differences in UK and US measures which were nominally the sam e. The UK inch

measured 2.53998 cm while the US inch was 2 .540005 cm. Both were standardised at 2.54 cm in July 1959, though the U S co ntinued to use 'their'

value for several years in land surveying work - this too is slowly being metricated.

In France the metric system officially started in June 1799 with the declared intent of being 'For all people, for all time'. The unit of length was the

metre which was defined as being one ten -millionth part of a quarter of the earth's circumference. The production of this standard required a very

careful survey to be done which took several years. However, as more accurate instruments became available so the 'exactness' of the standard

was called into question. Later efforts were directed at finding some absolute standard based on an observable physical phenomenon. Over two

centuries this developed into the S I. So m aybe their original slogan was more correct than anyone could have foreseen then.

Metric System of M easurements


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Length Area

10 millimetres = 1 centimetre 100 sq. mm = 1 sq. cm

10 centimetres = 1 decimeter 10 000 sq. cm = 1 sq. metre

10 decimetres = 1 metre 100 sq. metres = 1 are

10 metres = 1 decametre 100 ares = 1 hectare

10 decametres = 1 hectometre 10 000 sq. metres = 1 hectare

10 hectometres = 1 kilometre 100 hectares = 1 sq. kilometre

1000 metres = 1 kilometre 1 000 000 sq. metres = 1 sq. kilometre

Volume Capacity

1000 cu. mm = 1 cu. cm 10 millilitres = 1 centilitre

1000 cu. cm = 1 cu. decimetre 10 centilitree = 1 decilitre1000 cu. dm = 1 cu. metre 10 decilitres = 1 litre

1 million cu. cm = 1 cu. metre 1000 litres = 1 cu. metre

Mass

1000 grams = 1 kilogram

1000 kilograms = 1 tonne

The distinction between 'Volume' and 'Capacity' is artificial and kept here only for historic reasons.

A millitre is a cubic centimetre and a cubic decimetre is a litre. But see under 'Volume' for problems with the litre.

The U K (Imperial) System of Measurements

Length Area

12 inches = 1 foot 144 sq. inches = 1 square foot

3 feet = 1 yard 9 sq. feet = 1 square yard

22 yards = 1 chain 4840 sq. yards = 1 acre

10 chains = 1 furlong 640 acres = 1 square mile

8 furlongs = 1 mile

5280 feet = 1 mile

1760 yards = 1 mile Capacity

20 fluid ounces = 1 pint

Volume 4 gills = 1 pint

1728 cu. inches = 1 cubic foot 2 pints = 1 quart

27 cu. feet = 1 cubic yard 4 quarts = 1 gallon (8 pints)

Mass (Avoirdupois)

437.5 grains = 1 ounce Troy Weights

16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight

14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)

8 stones = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)20 cwt = 1 ton (2240 pounds)

Apothecaries' Measures Apothecaries' Weights

20 minims = 1 fl.scruple 20 grains = 1 scruple

3 fl.scruples = 1 fl.drachm 3 scruples = 1 drachm

8 fl.drachms = 1 fl.ounce 8 drachms = 1 ounce (480 grains)

20 fl.ounces = 1 pint 12 ounces = 1 pound (5760 grains)

The old Imperial (now UK) system was originally defined by three standard measures - the yard, the pound and t he gallon which were held in

London. They are now defined by reference to the S I measures of the metre, the k ilogram and the litre. These equivalent measures are exact.

1 yard = 0.9144 metres - sam e in US

1 pound = 0.453 592 37 kilograms - same in US

1 gallon = 4.546 09 litres - different in US

Note particularly that the UK gallon is a different size to the US gallon so that NO liquid measures of the same name are the same size in the UKand US systems.

Also that the ton(UK) is 2240 pounds while a ton(US) is 2000 pounds. These are also referred to as a long ton and short ton r espectively.

Metrication in the U K

There have been three major Weights and Measures Acts in recent times (1963, 1976 and 1985) all gradually abolishing

various units, as well re-defining the standards. All the Apothecaries' measures are now gone, and of the Troy measures,

only the ounce remains. The legislation decreed that -

From the 1st October 1995, for economic, public health, public safety and administrative purposes, only metric units

were to be allowed EXCEPT that -

y pounds and ounces for weighing of goods sold from bulky pints and fluid ounces for beer, cider, waters, lemonades and fruit juices in RETURNABLE containersy therms for gas supplyy fathoms for m arine navigation


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could be used until 31st December 1999.

The following could continue to be used WITHOUT time limit -

y miles, yards, feet and inches for road traffic signs and related measurements of speed and distancey pints for dispensing draught beer and cider, and for m ilk in RETURNABLE co ntainersy acres for land registration purposesy troy ounces for transactions in precious metals.

Sports were exempt from all of this, but most of them have (voluntarily) changed their relevant regulations into

statements of equivalent metric measures.

That was how the legislation was framed. In common usage the 'old' units are still very apparent.

HistoricalPerspectives on Metrication by Jim Humble

who was the last Director of the UK Metrication Board.

The first parliamentary reference to metrication in the UK was 13th April 1790. This was when parliamentarian Sir John Riggs Miller [Britain] and

the Bishop of Autum, Prince Talleyrand [France] put to the British Parliament and French Assembly respectively, the proposition t hat the two

countries should cooperate to equalise their weights and measures, by the joint introduction of the metric system.

There was no immediate progress although there were many positive debates in the second half of the 19th Century. For example, 1s t

July 1863 the Bill for a compulsory change to the metric system was approved by 110 votes to 75 votes. Speakers argued many of th e points we

hear today. On the one hand supporters argued its logic and simplicity, savings in time and money, advantages to trade and ed ucation. Opponents

stressed the undesirability of following the precedent of France and the problems of conversion for the illeducated and disadvantaged. However

no specific cut-off dates were proposed.

The following year, 9th March 1864, the House of Lords debated a Bill to permit the use of metric weights and measures in trade. One supporter

noted that Englishmen were not orious for liking old terms and old habits and he hoped that the new nomenclature would not be diverted by

attempts at ridicule. He said the sound of the word 'metric' can be absurd to anyone but a fool who has never heard it before ; but no more than a

'yard' to a man who has never heard of a 'yard' before.... !!! Parliament passed the Bill and this became the Metric Weights an d Measures Act

1864.

On the 24th February 1868 a parliamentary proposal to set Imperial cut -off dates was withdrawn on promise of a Royal Commission of enquiry.

The Enquiry Report was positive, and on the 26th July 1871 Britain almost became a metric country. The government lost the Bill to m ake metric

compulsory after two years, by only 82 votes to 77 votes. An argument that might ha ve influenced opponents was a plea that Britain would be

"letting down America and our colonies" who had harmonised their systems with the ones in use in Britain. [NB At that time th e American

Congress had emulated Britain by allowing contracts in metric. A particularly strong USA advocate for m etric was John Quincy Adams.]

There were further debates, and near misses, in the UK Parliament in 1872 and 1896, before a comprehensive debate [21st June - 6th

August 1897] concluded by legalising the use of metric for all purposes. There were no contrary votes. [NB This is the debate which most

references indicate to be the genesis of metrication in the United Kingdom.]

Metrication continued to be d ebated for the next 10 years. In 1904 The House of Lords unanimously voted to make metric compulsory after two

years. It was claimed that the Austrian and German nations had successfully made metric compulsory with a changeover time of only "one

week"!!!!! . The Gover nment said they would not obstruct the proposal, but the Bill was never adopted in the Commons. Two similar debates

in 1907 failed. By now, the Board of Trade was expressing some reservations, claiming that metrication had failed in France and that the

agricultural labourer would never ask for 0.56825 of a litr e of beer. The vote against compulsion rose to 150 votes to 118 votes. Conflicts in Europe

put further political consideration of metrication out of mind until the publication of a Government White Paper on Weights a nd Measures 10th

May 1951.

The 1951 White Paper was in fact the 28th Report put to Parliament during the preceeding 100 years. This latest report was in response to the the

Hodgson Committee Report published in1949. Eventually we had the Weights and Measures Act 1963; a long series of Parliament ary questions toMinisters and the Federation of British Industries [now the CBI] lobby in favour of metrication in 1965. These initiatives culminated with the

creation of the Metrication Board in 1969 by Anthony Wedgewood Benn, Minister of Technology. The target date for completion was end 1975.

The transition to metrication and the role of the Board were given positive support and encouragement by Geoffrey Howe the re sponsible Minister

of the new Government in 1972. Indeed at that time, and until circa 1977/8, there was good, sensible and steady progress which seemed to be

supported by every section of society including, for example, the small retailers and the elderly as represented by Age Conce rn.

Prepackaged food changed but the really difficult issue to emerge affected retailers of 'loose weight' products. They needed to be reassured there

would be an agreed cut -off date for their transfer from Imperial to metric. The retail problem was that metric prices would always appear to be

more expensive than the ir nearest Imperial equivalent. Voluntary transferees to metric found themselves comme rcially disadvantaged. This is

because viz. 4 ozs is smaller than 125 g: one pound is smaller than 500 g and a pint is smaller than a litre. Prices are corr espondingly lower. The

issue of how best to explain the position to consumers dominated m uch of the B oard's creative thinking.

The product which brought all voluntary retail initiatives to a full stop was the experience of the floor covering and carpet retailers.

Their 1975 change to sales by the sq. metre started well, but in 1977 one of the major High Street retailers found enormous commercial advantage

in reverting to sales by the square yard. Consumers could not be persuaded to believe that goods costing, for example, 10 per square yard or 12

per square metre were virtually priced the same. Consumers bought, in very significant volume, the apparently cheaper priced imperial version.

Metrication of carpet sales entered into full scale reverse and the Chambers of Trade and retail associations pressed for firm Governmentleadership i.e. compulsory cut -off. With hindsight one of the Metrication Board jingles may have helped spread the 'carpet' misunderstanding. This

was the jingle " a metre measures about three foot t hree , just a bit longer than a yard you see". Consumers understandably couldn't relate an e.g.

2 per square unit price difference with the Metrication Board's "just a bit longer". Then the political nerve began to fail.

Board of Trade Ministers Shirley Willia ms, Alan Williams and later Roy Hattersley and John Fraser supported metrication. They seemed to

recognise the setting of a cut -off date was unavoidable. They had had, by this time, the benefit of analysing the results of successful metric

changes in all the Commonwealth countries. There was a wealth of information within the Department of Trade to show that a clear retail cut -off

date was both desirable and inevitable....exactly as 19th Century parliamentarians had forseen. The necessary Order, drafted by the Board of Trade

in 1978, was agreed by a huge range of retail trade, industry, engineering, consumer, trade union, elderly person, sporting and educ ational

organisations and..... the overwhelming number of parliamentarians. A small number of c ritics, in each political party, did voice opposition to the

element of compulsion but this seemed to come from a relatively small minority within the Eurosceptic movement.

However, the initiative was in the hands of Secretary of State for Trade, Roy Hattersley and a General Election was expected in 1979. There

seemed to be weeks and weeks of "will he/ won't he" allow Parliament to vote for the Order giving the final Imperial cut -off. Almost every private

test of opinion indicated the Order would command a substantia l majority in Parliament. Although the Opp osition sensed a weakness in the

resolution of the Labour Government it was acknowledged that many conservative MPs had been career -long advocates for cut-off and would


14/21

therefore be likely to favour the Government Order, or at least abstain. In the event, Roy Hattersley chose not to test opinion, not to allow the

vote. He withdrew the draft Order. Speculation was that he judged the issue might lose some votes in the forthcoming election . Plenty of time to

introduce Imperial cut-off Orders after a Labour victory. The junior Trade Minister, John Fraser, made his disgust and disappointment apparent...

suggesting the actions of his Secretary of State would be seen as "gutless". Many shared that view. Labour lost the elec tion anyway and Margaret

Thatcher became Prime Minister.

One Conservative backbencher, Sally Oppenheim had been almost the lone but persistent critic of the metric programme. Ironica lly she was

appointed junior Minister of Consumer Affairs at t he DTI and t hen metrication was added to her portfolio. In letters to MP's and associations she

made it clear

[a] she was not opposed the metrication in principle,

[b] metrication was not the result of Britain's accession to the EEC but

[c] she did object to measur es which would compel people to adopt metric against their will. Proponents of metrication, trade and consumer

organisations, officials and the Metrication Board explained and argued that a voluntary change at retail level was absolutel y impossible...it could

never happen. It was a recipe for confusion, waste and duplication. Government had to lead over the last hurdle. It did, it l ed backwards.

In 1980 the Metrication Board was abolished.

In truth the Metrication Board had little else to do. Every possible programme had been agreed, consumer information campaigns composed and

there was nothing to do until or unless a date was fixed for the completion of the transition. We little knew then the die wa s set for a further 20

years of waste, confusion and argume nt. Successive DTI Ministers did nothing to inform consumers or public opinion. They did nothing to refute

the new 'big lie' namely, that Britain was being forced to change because of the European Commission. In fact, during the pas t 20 years most

Commission Officials, European Politicians and businesses in Continental Europe 'couldn't have given a damn' whether Britain changed to the

metric system or not. They seemed to quite like the idea of Britain shooting itself in its economic foot, by imposing upon i tself the extra costs and

waste of maintaining a dual system. For twenty years not one single British Minister has attempted to explain the advantages of metrication; been

frank about the changes which had successfully taken place in the rest of the World or the fact that we had committed ourselves to become a

metric nation long before we joined the European Community. Most tried to pretend or imply they were protecting our British c ulture from the

European bully.

How sad, what a waste, what a pity.

Jim Humble OBE

Director of the Metrication Board

[1978-1980]

Some other dates of note

1950 The Hodgson Report

was published which, after arguing all the points for and against, favoured a change to metric.

1963 Weights and Measures Act

defined the basic measures of the 'yard' and the 'pound' in terms of the 'metre' and the 'kilogram'. Many of the old imperial measures were

abolished (drachm, scruple, minim, chaldron, quarter, rod, pole, perch, and a few more)

1971 Currency was Decimalised

1985 Weights and Measures Act

abolished several more imperial measures for purposes of trade, and defined the 'gallon' in terms of the 'litre'.

Thus, all the measures had been m etricated even if the public hadn't!

The U S System of M easurementsMost of the US system of measurements is the same as that for t he UK. The biggest differences to be noted are in C apacity which has both liquid

and dry measures as well as being based on a different standard - the US liquid gallon is smaller than the UK gallon. There is also a measuremen t

known at the US survey foot. It is gradually being phased out as the maps and land plans are re -drawn under metrication. (The changeover is being

made by putting 39.37 US survey feet = 12 m etres)

Length Area

12 inches = 1 foot 144 sq. inches = 1 square foot

3 feet = 1 yard 9 sq. feet = 1 square yard

220 yards = 1 furlong 4840 sq. yards = 1 acre

8 furlongs = 1 mile 640 acres = 1 square mile

5280 feet = 1 mile 1 sq.mile = 1 section

1760 yards = 1 mile 36 sections = 1 township

Volume

1728 cu. inches = 1 cubic foot27 cu. feet = 1 cubic yard

Capacity (Dry) Capacity (Liquid)

16 fluid ounces = 1 pint

2 pints = 1 quart 4 gills = 1 pint

8 quarts = 1 peck 2 pints = 1 quart

4 pecks = 1 bushel 4 quarts = 1 gallon (8 pints)

Mass

437.5 grains = 1 ounce Troy Weights

16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight

14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)

100 pounds = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)

20 cwt = 1 ton (2000 pounds)


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Apothecaries' Measures Apothecaries' Weights

60 minims = 1 fl.dram 20 grains = 1 scruple

8 fl.drams = 1 fl.ounce 3 scruples = 1 dram

16 fl.ounces = 1 pint 8 drams = 1 ounce (480 grains)

12 ounces = 1 pound (5760 grains)

As with the UK system these measures were originally defined by physical standard measures - the yard, the pound, the gallon and the bushel.They

are now all defined by reference to the S I measures of the metre, the kilogram and the litre. These equivalent measures are exact.

1 yard = 0.9144 metres - same as UK

1 pound = 0.453 592 37 kilograms - same as UK

1 gallon (liquid) = 3.785 411 784 litres

1 bushel = 35.239 070 166 88 litres

Note particularly that the US gallon is a different size to the UK gallon so that NO liquid measures of the same name are the same size in the US

and UK systems.

Also that the ton(US) is 2000 pounds while a ton(UK) is 2240 pounds. These are also referred to as a short ton and long ton r espectively.

Note than in matters concerned with land measurements, for the most accurate work, it is necessary to establish whether the US survey measures

are being used or not.

Other Measures

barn

The barn is a very small unit of area used to express the cross -sectional area of the nucleus of an atom. It was defined in 1942 by Holloway and

Baker (in Chicago) and the name was taken from the expression "as big as a barn door" which it was, relatively speaking, in t heir particular work

with sub-atomic particles.

1 barn = 10-28

square metresLater, following on from that idea, the ' shed' an even smaller unit was defined, but this seems never to have b een taken up by the scientific

community.

1 shed = 10-24

barns = 10-52

square metres

barrel

The word 'barrel' is both a name for a type of container and also a unit of measure. As a container, the once very familiar barrel was made of wood

and roughly cylindrical in shape except that it 'bulged' outwards in the middle, and was used to transport not only the obvio us liquids (water, beer,

wine etc.) but also other commodities such as fish, sugar, flour, meat, cement, minerals, and so on. The sizes of the different barrels vari ed with

contents and, some of these different barrels acquired different names. So, deeper enquiry must be made if the exact quant ity meant in any

particular context is wanted. The sizes given here are to help the modern reader who wishes only to have a rough idea of just how big something

might have been.

Small numbers like 123 are the equivalent size to the nearest litre.

For liquids similar to water (wine etc) this is also the weight of the contents in kilograms.

barrel = 36 galls(UK) 164

butt = 108 galls(UK) 491

firkin = 9 galls(UK) 41

hogshead = 54 galls(UK) 245

kilderkin = 18 galls(UK) 82

pipe = 126 galls(US) 477

pin = 4.5 galls(UK) 20

puncheon = 70 galls(UK) 318

tierce = 42 galls(US) 159

tun = 216 galls(UK) 982

A study of the sizes shows the relationships between some of these containers.

Like: 1 tun = 2 butts = 4 hogsheads = 6 barrels = 12 kilderkins etc.

The use of the US gallon betrays the origins of the container as being in the wine trade. It was the old UK wine gallon which later became the

standard US liquid gallon.

The unit of a barrel as used in the oil trade is, in f act, the tierce which is one-third of a pipe. 'Tierce' and 'pipe' were used for both containers and

measures in the wine trade.

Some other names for barrel- like containers of unspecified size are

breaker cask drum keg tub

bels & decibels

Abbreviations are B and dB respectively.

The bel was originally a measure of sound intensity based on a logarithmic (base 10) scale. This means that each increase of 1 bel is 10 times louder

than the one before it. The need for such a scale is that the mea surement of noise covers such a big range. A really loud noise is billions of times

louder than a quiet one. On this logarithmic scale, one billion is only 9.

1 billion = 109

It is named after Graham A. Bell (1847 -1922) who invented the telephone.

However, it is the decibel (one-tenth of a bel) which is much better known and used. On this scale, a value of 0 dB represents the smallest amount

of sound that can actually be detected, 50/60 dB would be the level of ordinary conversation, and above 130 dB of noise would cause pain.

The dB logarithmic scale idea has since been adopted by other specialist areas, most notably in electronics. Here they use it to measure power.

Thus dBW for decibel watts, and dBmW for decibel milliwatts (in laser work) which, unhelpfu lly for us, they often write as dBm.

Some other (related) words are: neper phon sone

For much more detailed information on all of this,

go to the A to Z of units listed at (and linked from) the bottom.


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bottles

The bottle is a well -known container of all kinds of liquids. It is not a legally defined measure, though for certain purposes there is common

agreement on what size it should be. H owever there are different ways in which the capacities of bottles are stated. For instance, milk bottles give

it in litres, wine bottles in centilitres [cL] and smaller sizes of soft -drink bottles in millilitres [mL]. Of course there are marketing ploys at w ork here

~ 330mL sounds more tha n 33cL and certainly much more than 0 .33L !

How did the wine bottle come to be 75 cL in size? It has a long and complicated history but, briefly, in the 1600's when bottles were made by hand,

the wine bottle was about 46 .24 cubic inches (26 and two-thirds fluid ounces) in capacity, a measure which was known as a 'reputed quart'. This

came from being one -quarter of a wine gallon which was the size of 8 t roy pounds of wine. (Wine by the pound!) Metrication trimmed one and a

half teaspoonsful off this to m ake it 75cL.

One set of bottle sizes which always fascinate is that used for champagne. The names, with their generally accepted measures, are

bottle

= 1 bottle

= 75 cL

magnum

= 2 bottles

= 1.5 L

jeroboam

= 4 bottles

= 3 L

rehoboam

= 6 bottles

= 4.5 L

methuselah

= 8 bottles

= 6 L

salmanazar

= 12 bottles

= 9 L

balthazar

= 16 bottles

= 12 L

nebuchadnezzar

= 20 bottles

= 15 L

The large sizes are rarely used, except for very special

(and expensive) occasions when they ar e usually made to order.

Some other names of bottle -like containers are

amphora ampoule ampulla blackjack calabash chagal

demijohn flagon flask gallipot gourd phial vial

brix

A measure of the percentage of sucrose contained (by weight) in a sugar solution at a temperature of 17 .5C. It is measured by using a

saccharometer (=hydrometer) graduated in degrees of Brix, where 1 degree = 1%

It is important to know this value during the fermentation process of alcoholic d rinks (wines & beers) since the alcoholic content of the final liquid

is determined by the amount of sugar present at a certain stage.

The measure was devised by A F W Brix (1798 -1870) a German chemist.

BTU or Btu

Both are measures of energy. The BTU is the Board of Trade Unit and is equivalent to 1 kilowatt hour (kWh) but is no longer used. The Btu, or

BThU, is the British Thermal Unit (equivalent to over 3000 BTU's) which is obsolete but still seen quite a bit. The SI uni t of energy is the joule.

cable

This was a measure of length used at sea. In the UK it was defined as 100 fathoms (600 feet); and in the US as 120 fathoms (720 feet). Informally, it

was also regarded as one-tenth of a nautical mile (608 feet) in the UK. The unit is no longer used operationally, and neither is the fathom.

cholesterol

The level of cholesterol in one's blood is an important measure of the state of one's health, especially in terms of assessin g life expectancy.

Unfortunately, 2 different ways of measuring it are used.In the US it is given in mg/dL (milligrams per decilitre or 100 millilitres) while the UK uses mmol/L (millimoles per litre). To change from one system

to the other:

From US to UK units divide by 38.6

from UK to US units multiply by 38.6

As a rough guide to the sort of figures expected: in UK units it should be less than 5, while in US units the total should be less than 200.

Then there is the matter of goodand badcholesterol. But that has nothing to do with the units used to measure it.

cookery measures

What a mess! The system of measures that is. It must be realised that the measures used had their origins in the days when th e ordinary kitchen

had no specific measuring utensils (scales or graduated jugs) and recipes had to give the required amounts in terms of what would be to hand, like

'teaspoons' 'tablespoons' and 'cups'. Given that the sizes of such things did not vary very m uch in those times, and that rec ipes are basically only

about proportions between ingredients, it all worked very well.

A look now in almost any kitchen will show just how much these things can vary in size, and indicate that some sort of 'stand ardisation' is needed.

The simple answer is to give weights and volumes in regular measures (metric preferr ed) and avoid any reference to utensil measures. Or,

alternatively, specify what size those measures are intended to be. This latter is much better since many of the smaller quan tities would be quitedifficult to measure. Most cookery books nowadays usuall y include a section giving guidance on this topic.

Of course, that still leaves the problem of working from an old recipe.

As a guide, and nothing more than a guide, try

1 teaspoon = 5 mL

1 tablespoon = 15 mL = 3 teaspoons

1 cup = 250 mL (= one-quarter of a litre)

Of course, if it is a dry ingredient, then it is necessary to know whether the spoon is to be 'heaped' or 'level'

And then there are 'pinch' 'handful' & 'teacup'.

Never mind, think of cooking as an art, and not a science.

drops

This measure is much used in medicine for prescribing dosages for treating ailments of the nose, ear and throat. Surprisingly, the exa ct size of a

drop is NOT defined, but everyone 'knows' roughly what it means, though variations can be found in the literature.

In general, it can be taken that


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1 drop = 0.05 millilitres (mL)

which means 100 drops would fill a 5 mL teaspoon.

e

This symbol is now often seen on packaging which originates from within the European Union. It is NOT a unit of measurement.

It is a lower ca se 'e' which is printed adjacent to (before or after) the stated (nominal) quantity of the contents of the package. Th us

e 150g or 275mL e

It indicates that the quantity stated lies within the limits allowed by the rules given under

The Average System of Weights and Measures

eV

This stands for "electronvolt" and is a measure of energy used in nuclear and atomic physics. It is a very small unit and is more usually seen as keV,

MeV or GeV (that is kilo- m ega- and giga- eV).

1 eV = 1.602 176 462 10-19

joules

But, since this figure has to be determined by experiment, its value might be a little different in other printed sources (de pending on date of

publication).

fluid ounce

This is a measure of volume and not mass or weight. This is because it is def ined in relation to the gallon.

In the UK 160 fl.oz. = 1 gallon

In the US 128 fl.oz. = 1 gallon

This looks like a big difference but, the UK and US gallons are not the same size. C hanging to a common unit we have

In the UK 1 fl.oz. = 28 .413 063 mL

In the US 1 fl.oz. = 29 .573 530 mL

(A difference of about 4%)

The original intention (in both cases) had been to make the fluid ounce also equal to one ounce of wat er in weight. In fact

In the UK 1 fl.oz. = 1 .002 241 oz

In the US 1 fl.oz. = 1 .043 176 oz

Considering their closeness and that they are only (usually) used for non -scientific measurements it is not unreasonable to treat them as being the

same size and weighing 1 ounce.

But, if really pressed, there are (small) differences!

gauges

also gage or gages

This is one of the more overworked words in the English language. Major dictionaries identify over 15 different usages of thi s word!

First of all, for the use we make of it in connection with measuring, it is NOT a unit in itself. It can best be tho ught of as a collection of standard

sizes. Each collection having its own identity and not necessarily having any relationships within itself or with any other c ollection.

A characteristic of nearly all collections of gauge sizes is that t he size is given by a number and you need to refer to a table in order to find exactly

what size or dimension that number stands for. Neither do you know beforehand whether bigger numbers mean bigger (or smaller) sizes.

The standard sizes used for a collection are most oft en laid down by the ruling, or organising, body concerned with the use of whatever it is that is

being measured. It is most unusual for any gauge sizes to defined by government legislation. (Unlike, for instance, our measu res of weight, length

etc.)One of the better known examples of gauge sizes is that used for wire where there are such well -known names as American (or Brown &

Sharpe);Birmingham (or Stubbs);British Imperial (or S W G);

Gauge sizes are also used for sheet -metal, model railways, knitting a nd sewing needles, shot-guns, and several other things.

Though not usually referred to as gauge sizes, though in principle they are, we have those for clothes and shoe sizes, and th e Beaufort wind scale.

hand

This is a measure of length which, if nothing else, serves to remind us how many length -units had their origin as a part of the human body which

served as a convenient built-in measure to be used to size up something with a rough and ready degree of accuracy. For general use it has long

been obsolete, but it is still used to measure and record the height of a horse.

1 hand = 4 inches (just over 10 centimetres)

hoppus foot

This is a measure of volume once used in forestry work but now obsolete. It was derived from a formula used to find the volum e of usable wood in

the trunk of a tree, after an allowance had b een made for waste (about 20%).

1 Hoppus foot = 0.036 cubic metresThe unit was named after Edward H oppus, an English surveyor, who devised the system in 1736.

klicks

Also spelt klik or click.

It is principally a measure of length or distance, and is equal to 1 kilometre

There seems to be some doubt about when it first originated, but certainly was in wide use by the US military in the Vietnam War (1961 - 75).

It is also sometimes used to mean a speed of 1 kilometre per hour.

lb & oz

These are very well-known abbreviations for the pound and the ounce, but where did they come from?

When the Romans came to Britain they brought their own system of measures. For weighing they used the 'libra' and ' uncia' (which was one-

twelfth of a libra). When the English language was forming the word 'pund' appeared and was concerned with weighing, but slow ly changed (to

pound) to m ean the weight itself, which was the libra, and the abbreviation 'lb' was retained.

It is not hard to see how 'uncia' became 'ounce' but why 'oz'? Hazy! The 'best' story is that the merchants of those times we re always looking for


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contractions for frequently written words and for ounce wrote o+squiggle which got formalised over time into oz. (An example of early text-

messaging?)

But what about its size? There are not 12 ounces in a pound. Well not now. The original pound was the Troy p ound which did have 12 ounces.

Later the standardised pound Avoirdupois (7000 grains) was introduced, thi s was bigger than the Troy (5760 grains). But they decided to have 16

ounces in the pound which made the new ounce (437 .5) smaller than the old one (480).

Note that the 'uncia' as the one-twelfth part of a measure was retained in English measures as a divi sion of the 'foot' but in that case its name

evolved into 'inch'.

Inevitably, liberties have been taken in re -telling 2000 years of history in so few words!

In reality it was an evolutionary and very uneven process.

Going 'metric' is a doddle in comparison!

litre/liter

These are the same measure. The difference is only in the spelling. In UK English it is 'litre', in US En glish it is 'liter'.

There can be some ambiguity about the size of the litre. When the metric system was introduced in the 1790's the litre was intended to match up

with the volume occupied by 1 kilogram of pure water at a specified pressure and temperature. As the ability to measure thing s got better (by 100

years later) they found that there was a mismatch between the kilogram and the litre. As a result of this they had to redefine the litre (in 1901) as

being 1.000028 cubic decimetres. Very handy!

This nonsense was stopped in 1964 when it was ruled that the word "litre" may be employed as a special name for the cubic dec imetre, with the

additional recommendation that, to avoid any possible confusion,

'in high-accuracy work the name "litre" should not be used.'

So now the litre is taken as being a cubic decimetre, or

1 litre = 1000 cubic centimetres (= 1000 mL)

It should be remembered th at one unusual feature of the litre is its abbreviation. It is unique in that two forms are allowed. In 1979 the governing

body who control the SI ruled that the letter used as the abbreviation for litre could be written in either lower or upper ca se, 'l' or 'L', to avoid

possible confusion with '1'(one). They hoped one day to make a decision on one or the other, but have not done so yet. It see ms a pity that the 'L'

appears to be so little used. It is clearer on printed material (mL rather than ml) and cer tainly much the better way for written matter. Given the

number of cases that come to notice from time to time in medical work where a wrong dosage has been administered, perhaps it should be made

mandatory in that field at least.

mcg

Stands for "microgram" or one-millionth of a gram. It is not an 'officially' approved abbreviation. It should be written g

However, the difficulties of printing the Greek letter "" led to the use of "mcg". Nowadays there is rarely a real need for this; it is largely a matt er

of laziness.

metre/meter

These are the same measure. The difference is only in the spelling. In UK English it is 'metre', in US English it is 'meter'.

No matter how it is spelt, it is the standard by which all other measures of length are defined. For example a 'foot' is 0 .3048 of a metre and so on.

One advantage of the UK form is that it allows a clear distinction to be made between the 'micrometre' which is one -millionth of a metre and a

'micrometer' which is an instrument used (mainly by engineers) to measure small sizes with great accuracy.

micron

symbol (the Greek letter mu)"Micro" means one-millionth and the word micron means one -millionth of a metre. It is often used as a measure of thickness for sheet metal and

card.

It is still in very com mon usage though no longer an approved SI unit.

It should be "micrometre" or m.

miner's inch

This is NOT a measure of length, but of the rate of water flow in a miner's sluice. A sluice is used in getting metallic ores (like gold) from the gravel

containing them by a system of washing in which the rate of flow of the water is very important. Too fast and it takes away everth ing, too slow and

nothing happens.

1 miner's inch is a flow of 1 .5 cubic feet per minute or about 64,000 litres in 24 hours.

nail

As a measure this is now obsolete. It was once used as a measure of length for cloth, and was equal to one -sixteenth of a yard (two and a quarter

inches). It was also a measure of weight for wool or beef and equivalent to 8 pounds. Its alternative name was a 'clove'.

Where the 'nail' is a type of fastener (for wood) it picked up another measure in US usage. The size of the nail was expresse d by the cost (inpennies) of 100 nails of that size. Thus a one -inch nail would have been two-penny nail, while a four-inch nail would have been a twenty-penny nail

and so on.

rod, pole or perch

These have meant different things at different times and in different countries! But most commonly they may be taken to be al ternative names for

the same unit of length, and equal to 5 yards or 16 .5 feet. Sometimes the 'rod' being referred to is meant to be a unit of area, and it will be

necessary to read the context carefully to see if this is so. In that case it is equal to 272 .25 square feet.

They are now obsolete, but do seem to come up q uite often.

For more detailed information on these measures, look u nder 'rod' in

the A to Z of units listed at (and linked from) the bottom.

teaspoon

This common h ousehold implement has long bee n used as a measure of dosage when dispensing medicine at home. So what size was it? Well it

varied, there was no standard until about the middle of the last century when it was set (by general agreement) at 5 millilitres (5mL) and, to make


19/21

sure, free plastic "teaspoons" were given away with the appropriate medicine.

This is fine with liquids but what about a medicine which is in the form of granules or powder? Should it be a level measure or a heaped one? The

latter can be twice the size of the former! One manufacturer (of supplements) when challenged on the amount of the various ingredients in a dose

argued that a heaped teaspoon was needed, but it did not say so on the package. So, ask!

And then there is the teaspoon used in cookery . . .

Meanwhile the US National Institute of Standards and Technology give a teaspoon as 4 .928 922 mL (An example of spurious accuracy that is hard

to beat!)

verst

This is a Russian measure of length (now obsolete) equal to a little more than a kilometre (1.067 km) or about two -thirds of a mile.

English Customary Weights and Measures

Distance

In all traditional measuring systems, short distance units are based on the dimensions of the human body. The inch represents the width of a

thumb; in fact, in many languages, the word for "inch" is also the word for "thumb." The foot (12 inches) was originally the length of a human foot,

although it has evolved to be longer than most people's feet. The yard (3 feet) seems to have gotten its start in England as the name of a 3 -foot

measuring stick, but it is also understood to be the distance from the tip of the nose to t he end of the middle finger of the outstretched hand.

Finally, if you stretch your arms out to the sides as far as possible, your total "arm span," from one fingertip to the other , is a fathom (6 feet).

Historically, there are many other "natural units" of the same kind, including the digit (the width of a finger, 0.75 inch), the nail (length of the last

two joints of the middle finger, 3 digits or 2.25 inches), the palm (width of the palm, 3 inches), the hand (4 inches), the shaftment (width of the

hand and outstretched thumb, 2 palms or 6 inches), the span (width of the outstretched hand, from the tip of the thumb to the t ip of the little

finger, 3 palms or 9 inches), and the cubit (length of the forearm, 18 inches).

In Anglo-Saxon England (before the Norman conquest of 1066), short distances seem to have been measured in several ways. The inch ( ynce) was

defined to be the length of 3 barleycorns, which is very close to its modern length. The shaftment was f requently used, but it was roughly 6.5

inches long. Several foot units were in use, including a foot equal to 12 inches, a foot equal to 2 shaftments (13 inches), a nd the "natural foot" (pes

naturalis, an actual foot length, about 9.8 inches). The fathom was also used, but it did not have a definite relationship to the othe r units.

When the Normans arrived, they brought back to England the Roman tradition of a 12 -inch foot. Although no single document on the subject can

be found, it appears that during the reign of Henry I (1100 -1135) the 12-inch foot became official, and the royal g overnment took steps to make

this foot length known. A 12 -inch foot was inscribed on the base of a column of St. Paul's Church in London, and measurements in this unit were

said to be "by the foot of St. Paul's" ( de pedibus Sancti Pauli). Henry I also appears to have ordered construction of 3 -foot standards, which were

called "yards," thus establishing that unit for the first time in England. William of Malmsebury wrote that the yard was "the measure of his [the

king's] own arm," thus launching the story th at the yard was defined to be the distance from the nose to the fingertip of Henry I. In fact, both the

foot and the yard were established on the basis of the Saxon ynce, the foot being 36 barleycorns and the yard 108.

Meanwhile, all land in England was tr aditionally measured by the gyrdor rod, an old Saxon unit probably equal to 20 "natural feet." The Norman

kings had no interest in changing the length of the rod, since the accuracy of de eds and other land records depended on that unit. Accordingly, the

length of the rod was fixed at 5.5 yards (16.5 feet). This was not very convenient, but 5.5 yards happened to be the length o f the rod as measured

by the 12-inch foot, so nothing could be done about it. In the Saxon land-measuring system, 40 rods make a furlong (fuhrlang), the length of the

traditional furrow (fuhr) as plowed by ox teams on Saxon farms. These ancient Sax on units, the rod and the furlong, have come down to us today

with essentially no change. The chain, a more recent invention, equals 4 rods or 1/10 furlong in order to fit nicely with th e Saxon units.

Longer distances in England are traditionally measured in miles. The mile is a Roman unit, originally defined to be the length of 1000 paces of a

Roman legion. A "pace" here means two steps, right and left, or about 5 feet, so the mile is a unit of roughly 5000 feet. For a long time no one fel t

any need to be precise about this, because distances longer than a furlong did not need to be measured exactly. It just didn' t make muchdifference whether the next town was 21 or 22 miles away. In medieval England, various mile units seem to have been used. Eve ntually, what

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