Find radius, diameter, circumference, and area from any one value.
Circumference = 2πr; area = πr²; diameter = 2r.
A circle with radius 5 has a circumference of about 31.4 and an area of about 78.5.
You can enter radius, diameter, circumference, or area, and the calculator derives the rest.
The calculator uses pi to standard floating-point precision.
It uses whatever units you enter; keep them consistent.