Calculators

Calculate the area of a circle

Type the circle's radius into the box, and the calculator works out the area straight away. You can use either a comma or a full stop for decimals, like 4.5.

What is the area of a circle?

The area is how much space the circle takes up. The radius $r$ is the distance from the centre of the circle out to its edge.

The formula is:

A = \pi \cdot r^2

You multiply the radius by itself and then by $\pi$ . Pi is a fixed number, about 3.14, that is the same for every circle: it is the ratio between a circle's circumference and its diameter. Because the radius is multiplied by itself, doubling the radius makes the area four times as big.

Example

A circle has radius $r = 5$ . The area is:

A = \pi \cdot r^2 = \pi \cdot 5^2 = 25 \cdot \pi

So the area is $25 \cdot \pi$ , which is about 78.54 units².

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What is the area of a circle?

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