Use this calculator to find the area, circumference or radius of a circle. Given any one variable of a circle you can calculate the other 2 unknowns.
* Units: Note that units of length are shown for convenience. They do not affect the calculations. The units are in place to give an indication of the order of the results such as ft, ft2 or ft3. Any other base unit can be substituted.
Radius and Diameter:
r = d/2
Area of a circle:
A = πr2 = πd2/4
Circumference of a circle:
C = 2πr = πd
Using the formulas above and additional formulas you can calculate properties of a given circle for any given variable.