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.
Click here to see a proof that this is always true for any circle.
To find out more about circles, check out these books from Amazon.com or from your library: