Area of a Circle

Area of a Circle

GCSE(F), GCSE(H),

When the radius of a circle is known, the are of the circle can be calculated using a formula.

The formula is `A = pir^2`, where π is 3.14 and r is the radius of the circle.

If the diameter is known, the radius can be found by halving the diameter.

The area is an area measurement, and the answer will be in cm2, m2, etc.

Examples

1. What is the area of the circle, below?

Answer: 706.5 cm2

Area of a circle = `pir^2`

`A = pi xx 15^2`

A = 706.5 cm2

2. What is the diameter of a wheel, if the area is 500 cm2? Give your answer to the nearest centimetre.

Answer: 13 cm

`Area = pir^2`

`500 = pi xx r^2^`

159.24 = r2

r = 12.62, or 13 cm to the nearest cm.