Circumference to Diameter Calculator

About this calculator

Given a circle's circumference (C), its diameter is found by rearranging the classic formula C = πd into d = C / π. From there, the radius is simply half the diameter (r = d/2), and the area follows from A = πr², giving three related measurements from a single circumference reading.

This calculation is common whenever only the outer edge of a circular object can be measured directly — wrapping a tape measure around a tree trunk, a pipe, a wheel, or a tank — and the diameter, radius or area needs to be known. Students verifying geometry homework, engineers sizing pipes, and hobbyists building round objects from a measured wrap all rely on the same π-based relationship.