Circumference calculator

Calculate the circumference (perimeter) of a circle. Enter the radius or diameter.

Radius

Circumference formulas

From radius: C = 2πr

From diameter: C = πd (since d = 2r)

From area: C = 2√(πA)

What is π?

π (pi) ≈ 3.14159265... It's the ratio of any circle's circumference to its diameter. It's an irrational number — its decimal expansion never ends or repeats.

Example

Circle with radius 5: C = 2π(5) = 10π ≈ 31.4159