# Circumference of a Circle

How to solve the circumference of a circle problems: formulas, examples, and their solutions.

## Formulas

*C* = 2*πr**C*: circumference of a circle*r*: radius of a circle*π*: 3.141592...

*C* = *πd**C*: circumference of a circle*d*: diameter of a circle*π*: 3.141592...

This is true because *d* = 2*r*.

## Example 1

*r* = 5*C* = 2⋅*π*⋅5

## Example 2

*d* = 13*C* = *π*⋅13