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Electrical Power Calculators The following calculators are provided to help you determine the size of generator required foryour specific application. Other calculators on this page are for unit conversions and other powerrelated calculations.
Calculation
Power Calculator
Converting kVA to kW
Converting kW to kVA
Converting kW to HP
Amperes when kVA isknown
kVA Required to runmotors
Guide to StandardUints
Kilo Volt Amperes kVA
KiloWatts (1000watts = 1 kW)
kW
Ampere (Volt-Amperes orCurrent)
I
Volts E
Power Factor PE
Percent Efficiency %EFF
Horse Power HP
Power Requirement Calculator
Phase
VoltsRequire
dV
AmperesI
PowerFactor =
PowerkW
1
3
.8
1.
0
Converting kW to kVA
kW = kVA
Converting kVA to kW
kVA = kW
Converting kW to HP
kW = HP
What size genset isneeded to start a 3 phaseelectric motor Direct onLine (DOL) start
HP of
Motor =
GeneratorkVA
Required
Calculating Amperes (when you knowkVA)
Phase
Generator
VoltsRequire
= AmpereI
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1,2,3 kVA d
Standard Electrical Formulas Used for Power Consumption Calculations
TO DETERMINE: SINGLE-PHASE THREE-PHASEDIRECT
CURRENT
KVAI x E1000
I x E x 1.731000
--------
KilowattsI x E x PF
1000I x E x 1.73 x PF
1000I x E1000
Horsepower I x E x %EFF x PF746 I x E x 1.732 x %EFF x PF746 I x E x %EFF746
Amperes (when HP is known)HP x 746
E x %EFF x PFHP x 746
1.73 x E x %EFF x PFHP x 746E x %EFF
Amperes (when kW is known)KW x 1000
E x PFKW x 1000
1.73 x E x PFKW x 1000
E
Amperes (when KVA is known)KVA x 1000
EKVA x 1000
1.73 x E
Total Power Calculation
This web page can be used to calculate the total power (kva) of a single phase or three phase load. Use Tableone for three phase calculations, and use Table two for single phase calculations. The three phase loadcalculations assume the load is balanced.
Table 1 - Calculation of Total Power Three Phase Loads
Known Variables: Voltage, Current
Input System Line-Line Voltage (kv)
Input line current (amps)
Calculated Total Power (kva)
Compute
Known Variables: Real Power, Reactive Power
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Input Three Phase Power (kW)
Input Three Phase Reactive Power (kvar)
Calculated Total Power (kva)
Compute
Table 2 - Calculation of Total Power Single Phase Loads
Known Variables: Voltage, Current
Input System Line to Neutral Voltage (kv)
Input Line Current (amps)
Calculated Total power (kva)
Compute
• Formulas and calculations •
The relationship between
Electrical voltage V , amperage I , resistivity R, impedance Z,wattage P
Electricity and ElectricCharge
The nominal impedance Z = 4, 8, and 16 ohms (loudspeakers) is often assumed as resistance R.Ohm's law equation (formula): V = I × R and the power law equation (formula): P = I × V .
P = power, I or J = Latin: influare, international ampere, or intensity and R = resistance.
V = voltage, electric potential difference or E = electro motive force (EMF = voltage).
Enter any two of the following values and click the calculation button.The missing values will be calculated. Enter only two values.
The used Browser unfortunately supports no Javascript.
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The program is indicated, but the actual function is missing.
Voltage or volt E or V = volts V
Amperage or current I = amperes, amps A
Resistivity or resistance R = ohms Ω
Wattage or power P = watts W
For R take impedance Z reset
Fundamentals: Electric Laws − Formulary − Equations
Formula wheel ▼ Important formulasElectrical engineering laws Electronic engineering laws
V comes from "voltage" and E from "electromotive force". E means also energy,
so V is chosen.
The Big Power FormulasElectrical and mechanical power calculation
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Formula 1 − Electrical (electric) power equation: Power P = I × V =
R × I 2 = V 2 ∕ R
where power P is in watts, voltage V is in volts and current I is in
amperes (DC).
If there is AC, look also at the power factor PF = cos φ and φ = power factor angle(phase angle) between voltage and amperage.
Formula 2 − Mechanical (mechanic) power equation: Power P = E ∕ t
= W ∕ t
where power P is in watts, Energy E is in joules, and time t is in
seconds. 1 W = 1 J/s.
Power = force times displacement divided by time P = F · s / t or:
Power = force times speed (velocity) P = F · v.
Electric (electrical) Energy is E = P × t − measured in watthours, or
also in kWh.
Undistorted powerful sound is not to find in these formulas. Please,mind your ears!The eardrums are really only moved by the waves of the sound
pressure. That does notdo neither the intensity, nor the power or the energy. If you are in the
audio recordingbusiness, it is therefore wise not to care much about the energy,
power and intensity.
Very loud sounding speakers should have much power, but lookcloser at the veryimportant efficiency of loudspeakers. This includes the typical
question:How many decibels (dB) are actually twice or three times as
loud?There is really no RMS power. The words "RMS power" show not
correct, that there is acalculation of a power which is the multiplication of a voltage RMS
and an amperage RMS.RMS watts is meaningless. In fact, we use that term as an extreme
shorthand for power inwatts calculated from measuring the RMS voltage. Please, read here:Why there is no such thing as 'RMS watts' or 'watts RMS' and
never has been.Power is the amount of energy that is converted in a unit of time.
Expect to pay more whendemanding higher power.
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Tip: The electrical power triangle (power formula)
The magic triangle can be used to calculate all formulas of the "electric power law". You hide with
a finger the value to be calculated. The other two values show then how to do thecalculation.
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Please enter two values, the third value will be calculated.
Electric Power P: watts
Voltage V : voltsAmperage I : amps
reset
Calculations: Ohm's law - Ohm'smagic triangle
ALTERNATING CURRENT (AC) ~
V l = line voltage (volts), V p = phase voltage (volts), I l = line current (amps), I p = phase current (amps)
Z = impedance (ohms), P = power (watts), φ = power factor angle, VAR = volt-amperes (reactive)
Current (single phase): I = P / V p×cos φ Current (3 phases): I = P / 3 √ V l×cos φ or I = P / 3 V p×cos φ
Power (single phase): P = V p× I p×cos φ Power (3 phases): P = 3 √ V l× I l×cos φ or P = 3 √ V p× I p×cos φ
Power factor PF = cos φ = R/(R2 + X2)1/2, φ = power factor angle. For the purely resistive circuit, PF = 1
(perfect).
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3 Phase Circuit Calculations
Star Connection
Figure 1 Figure 2
Figure 1 shows three loads connected in the star formation to a three phase four wire supply system.Figure 2 shows the phasor diagram, the red to neutral voltage URN is taken as reference and the phasesequence is red, yellow, blue so that the other line to neutral voltages or phase voltages lie as shown.
If URN = UYN = UBN and they are equally spaced the system of voltage is balanced. Let UL be the voltage between any pair of lines (the line voltage) and UP = URN = UYN = UBN (the phasevoltage)
Then UL = 3UP
and IL = IP
where IL is the current in any line and IP is the current in any load or phase. The power per phase is P= UPIPcosØ and the total power is the sum of the amount of power in each phase
If the currents are equal and the phase angles are the same as in figure 3 the load on the system isbalanced, the current in the neutral is zero and the total power is
P = 3UL IL cosØ
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Figure 3
Delta Connections
Figure 4 Figure 5
Figure 4 shows three loads connected in the delta or mesh formation to a three phase supply system.Figure 5 shows the phasor diagram of the line voltages with the red to yellow voltage taken asreference.
The voltage applied to any load is the line voltage UL and the line current is the phasor differencebetween the currents in the two loads connected to that line. If the load currents are all equal and makeequal phase angles with their respective voltages the system is balanced and
IL = 3IP
The total power under these conditions is
P = 3UL IL cosØ