Enter a radius or diameter into the calculator below to determine the circumference and area of a circle.

## Circumference Formulas

The following two formulas are used by this calculator to determine the circumference.

C = pi * D

Where C is the circumference, pi is approximately 3.14159, and D is the diameter

C = 2 * pi * 4

Where C is the circumference, pi is approximately 3.14159, and r is the radius.

Additionally, this calculator determines the area of this circle using the following formulas.

A = pi * r^2

Where A is the area, and r is the radius

A = pi * (D/2)^2

Where A is area and D is the diameter