Circle Calculator

Circle properties and formulas

A circle is fully described by any one of its four properties: radius (r), diameter (d = 2r), circumference (C = 2πr), and area (A = πr²). Enter any one and this calculator derives the other three instantly using π ≈ 3.141592653589793. Results are shown to 8 significant figures.

For triangle calculations, see the Triangle Calculator. To convert area units, use the Area Converter.