Find the Areas of Circles Using Their Diameters

This activity is about finding the areas of circles, given their diameters.

You need to learn this important formula for a circle of radius, r :

Area of a circle = π r²

Remember that the radius is half the diameter.

Example

Find the area of a circle of diameter 12 cm.

Answer

First, work out the radius, which will be 12 ÷ 2 = 6 cm

Area = π r² =  π x 6² = π x 36 = 113.1 cm²  (1 dp)

Let's have a go at some questions now.