## About This Tool

The online Circle Calculator is used to calculate the area, circumference, diameter or radius of a circle. Given any one variable of a circle you can calculate the other 3 unknowns.

## Formulas

The following is the calculation formulas of the area, circumference and diameter of a circle whose radius is *r*:

The diameter of a circle

d = 2r

The circumference of a circle

C = 2πr = πd

The area of a circle

A = πr^{2}

Where:

A = area of circle

C = circumference of circle

d = diameter of circle

r = radius of circle

π = 3.141592654