You have already learned about the parts of circles and how to calculate circumference, diameter, and radius of circles.

In this activity, you will practise calculating the area of circles.  

Think about This:

Sometimes people decide to build rooms that are shaped like a circle. It is important to know how much area this takes up so that you can purchase enough materials for the floor, among other things.

Finding the Area of a Circle

Looking at the image of the circle above, you can see the straight line that goes from one side of the circle to the other through the centre of the circle. Remember that this is called the diameter of the circle. As you can see in the above image, the diameter of this circle is 10 cm.

However, to calculate the area of a circle, we need the radius. Remember also that a radius is a line that goes from the centre of the circle out to the edge. It is also half of the diameter. The radius of the circle above is 5 cm, as shown below.

In order to find the area of a circle, we can use the formula:




We can use this formula to find out the area of a circle if we know the radius. We can also use this formula to find out the radius of a circle if we know the area.

For example, the circle above has a radius of 5 cm, and if we were asked to find the area, we can use the formula to find the answer.

Try This:

1. Determine the area of the circle below.

Courtesy of ADLC

  Self-check!