# Area of a Circle

The area of a circle is the flat surface inside its circumference. The area is always equal to the radius squared, multiplied by π (pi).

Here's a proof that this is always true for any circle.

## Learn by doing: figure out the area of some circles around you.

Radius

Diameter

Circumference of a Circle

More about Geometry

## Bibliography and further reading about circles:

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Copyright 2012-2015 Karen Carr, Portland State University. This page last updated September 2015.

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