Circumference - Geometry Made Easy answers questions

Circumference of a Circle

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.
Area of a Circle
More about Geometry

Bibliography and further reading about circles:

More Geometry
More about Math home

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

Help support! (formerly "History for Kids") is entirely supported by your generous donations and by our sponsors. Most donors give about $10. Can you give $10 today to keep this site running? Or give $50 to sponsor a page?

For the US election, check out' page on the Constitution. From the Revolution on, people have fought for the right to vote. In the 1800s, Andrew Jackson got poor white men the vote; the Civil War and Lincoln brought the vote to African-American men. In the 1900s, women got the vote, and Martin Luther King Jr. fought to force white people to actually let black people vote.