Circle Calculator

About this calculator

This calculator takes a circle's radius and computes its area, circumference and diameter using the standard geometric formulas built around π (pi) — area equals π times radius squared, circumference equals 2π times radius, and diameter is simply twice the radius. Entering just the radius is enough to derive all three related measurements at once.

It is used across schoolwork, where students verify geometry homework or check their own manual calculations, as well as in practical situations like figuring out how much material is needed to cover or fence a circular area, sizing a round tabletop, pipe or garden bed, or working out how much fencing or edging trim is required around a circular perimeter. Anyone who only knows one dimension of a circle — commonly the radius from a spec sheet or measurement — uses this to get every other figure without doing the π arithmetic by hand.