Perimeter of a circle
Circumference is the circular version of perimeter: the distance around the outside edge.
Example
If the radius is 5, the circumference is 2 x pi x 5, or about 31.42 units. The diameter is 10.
When to use circumference
Use circumference when estimating a circular border, rim, belt length, edging or the distance around a round object. Use circle area when estimating the space inside the circle.
Common mistakes
If you know diameter instead of radius, do not enter the full diameter as radius. Divide diameter by 2, or use a calculator that asks for diameter directly.
Last reviewed: 2026-05-17