Circle Calculator

Enter any single value — radius, diameter, circumference, or area — and the rest fall out.

Properties

Radius

—

Diameter

—

Circumference

—

Area

—

The formulas

C = 2πr · A = πr² · d = 2r

Every circle property is a function of the radius. Knowing any one of these four lets you back-solve for the radius:

From diameter: r = d / 2
From circumference: r = C / (2π)
From area: r = √(A / π)