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Circumference - Geometry Made Easy
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Circumference of a Circle

Radius
Circumference of a circle

The circumference of a circle is the distance all the way around the circle. It's the same as the perimeter, but a special word that we only use for the perimeter of a circle. The circumference is always equal to twice the radius of the circle times π (pi), or 2πr.

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

Learn by doing: figure out the circumference of a plate in your kitchen.
Radius
Diameter
Area of a Circle
More about Geometry

Bibliography and further reading about circles:

More Geometry
More about Math
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Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

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