Work out circle diameter from circumference instantly with clear inputs, formula shown and shareable results.
Because C = πd, dividing a measured circumference by π recovers the diameter — the standard trick for sizing a pipe or tree trunk from a tape measurement around it.
Diameter
d = C / π, r = C / (2π)
Area from circumference
A = C² / (4π)
31.415927 / π = 10 exactly, so the radius is 5.
Yes. Foresters measure girth at breast height and divide by π to get diameter.