# 2.3 Area of a circle

The formula to find the area of a circle is similar to the one you have already used to find the circumference.

Area of a circle = pi × radius

^{2}*A*=*π**r*^{2}

## Box _unit5.2.1

**Hint:** Remember that when you square a number you simply multiply it by itself, radius^{2} is therefore simply radius × radius.

Let’s look at an example.

In the circle above you can see that the radius is 8 cm. To find the area of the circle we use:

*A*=*π r*^{2}*A*= 3.142 × 8 × 8*A*= 201.088 cm^{2}

Before you try some on your own, let’s take a look at one further example.

This circle has a diameter of 12 cm. In order to find the area, you first need to find the radius. Remember that the radius is simply half of the diameter and so in this example radius = 12 ÷ 2 = 6 cm.

We can now use:

*A*=*πr*^{2}*A*= 3.142 × 6 × 6*A*= 113.112 cm^{2}

Try a couple of examples for yourself before moving on to the next part of this section.

## Activity _unit5.2.3 Activity 6: Finding the area of a circle

Find the area of the circle shown below. Give your answer to one decimal place.

You are designing a mural for a local school and need to decide how much paint you need. The main part of the mural is a circle with a diameter of 10 m as shown below. Each tin of paint will cover an area of 5 m

^{2}. You will need to use two coats of paint. How many tins of paint should you buy?

### Answer

Using the formula:

*A*=*πr*^{2}*A*= 3.142 × 4 × 4*A*= 50.272 m^{2}*A*= 50.3 m^{2}to 1 d. p.

You need to find the area of the circle first. Since the diameter of the circle is 10 m, the radius is 10 m ÷ 2 = 5 m.

Using the formula:

*A*=*πr*^{2}*A*= 3.142 × 5 × 5*A*= 78.55 m^{2}

So the area of the circle you need to paint is 78.55 m

^{2}Since you need to give 2 coats of paint, you need to double this number:

78.55 × 2 = 157.1 m

^{2}

You now need to work out how many tins of paint you need. As one tin of paint covers 5 m

^{2}you need to do:157.1 ÷ 5 = 31.42 tins

Since you must buy whole tins of paint, you will need to buy 32 tins.

You have now learned all you need to know about finding the area of shapes! The last part of this section is on finding the volume of solid shapes – or three-dimensional (3D) shapes .

## Summary

In this section you have learned:

that area is the space inside a two-dimensional (2D) shape or space

how to find the area of rectangles, triangles, trapeziums and compound shapes

how to use the formula to find the area of a circle.