Circumference Calculator

What You Need to Know

A circle is a closed curve where every point is the same distance from the center. The circumference is the length of that curve — the distance you would travel if you walked around the circle once.

The circumference is denoted by C.

Radius (R) — the distance from center to any point on the circle.

Diameter (d) — the distance across the circle through the center. d = 2R.

Pi (π) — the ratio C/d, approximately 3.14159. Every circle, regardless of size, has this same ratio.

Circumference Formulas

From radius:

C = 2πR

From diameter:

C = πd

From area:

C = 2√(πS)

where S is the area of the circle.

This last formula comes from substituting R = √(S/π) into C = 2πR.