Finding the circumference of a circle.
We discovered that if you take a circles diameter and put it round the outside of a
circle it goes around 3 and a bit times.
This 3 and a bit has been worked out. It is actually a very long number. It is called Pi. It
also has a special symbol.
We will be using 3.14
So, to find the circumference of a circle we can take the diameter of a circle and multiply
it by Pi.
C = πd !
Can you show a formula of how you can find the circumference of a circle from its radius.
You can find also find the circumference by taking the radius, doubling it (this will give you the diameter and then multiply it by Pi.
C = 2πr !!
Use 3.14 for PiRadius Diameter Circumference
(Calculated)Circumference
(Measured) Difference
4cm
8cm
5cm
6.5cm
7cm
18cm
12cm
15cm
20cm
Extension
• Finding a radius/diameter when given a circumference.
• Finding the circumference of a semi-circle, quarter circle.