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.