Circumference of a Circle

Formula for circumference with examples

The circumference of a circle is the edge or rim of a circle itself. It is the equivalent of 'perimeter' for a circle. In other words, if you took a circle and unrolled it, you would have its circumference. You can use either of the formulas below to find circumference of a circle. One formula use the radius of a circle; the other formula uses the diameter.

Formula for Circumference
= 2Πr where r is the radius of a circle.
alternately,
circumference Formula
= d• Π where d is the diameter of a circle.

**These two formulas are just two different ways of finding the same thing (circumference) because the diameter of a circle =2• radius. So you should make use of whichever formula is more convenient. If you know a circle's radius, use the first version of the formula; if you know the diameter, use the second

This Page: Practice Problems | circumference formula
Related Pages:: Circles Home | Area of Circle

The rotating line on the left is an example of a circle's radius.

If the radius of a circle is 1 inch (1"), then the circumference of the circle = 2Π• 1" ≈ 6.28"

Practice Problems

Problem 1) What is the circumference of the circle below.

Circumference

Problem 2) What is the circle's circumference?
circumference of 9 inch circle

Circumference

Problem 3) What is the circumference of the circle pictured below?
circumference practice problem

Circumference

Problem 4) What is the circumference of a circle with a radius of 5"?

Circumference

Practice Problems (Medium)

Problem 5) A circle's circumference is (22Π)". What is the radius of this circle?

Radius

Problem 6) A circle's circumference is (102Π)". What is the diameter of the circle?

Diameter

Circumference of a Circle

Formula for circumference with examples

Formula for Circumference

circumference Formula