Math Calculators

Circumference to Radius Calculator

Calculate a circle's radius, diameter and area starting from its circumference, in the unit of your choice.

Radius —

Diameter —

Area —

About the Circumference to Radius Calculator

If you know a circle's circumference, you can work backward to find its radius, diameter and area by rearranging the standard circle formulas. The circumference input and each result carry their own unit selector, so you can measure in one unit and read results in another.

Formula: Radius = Circumference ÷ 2π · Diameter = Circumference ÷ π · Area = π × Radius²

This is useful whenever circumference is the only measurement available, such as measuring a tree trunk or pipe with a tape measure.