Find Circumferences of Circles Using Their Radii (1)

This worksheet is about finding the circumferences of circles.

The circumference of a circle is its perimeter or the distance around its edge.

 

You must learn these two important formulae for a circle of radius, r or diameter, d:

 

Circumference of a circle = 2πr

Circumference of a circle = πd

 

 

 

Example 1

Find the circumference of a circle of radius 6 cm.

 

Answer

Circumference = 2 × π × r = 2 × π × 6 = 12 × π = 37.7 cm  (1 decimal place)

 

 

Example 2

Find the circumference of a circle of diameter 6 cm.

 

Answer

Circumference = π × d = π × 6 = 18.8 cm  (1 decimal place)

 

Use a scientific calculator to work out your answer.  If you don't have one in the house, you can access one online.