# Circumference

## Circumference

The length of the outside edge of certain geometric figures.

### Formulas

The calculate the circumference C of a circle as a function of its diameter d, we can use the equation : $${C} = πd$$.

To calculate the circumference C of a circle as a function of its radius r, we can use the equation : $${C} = 2πr$$.

### Historical note

The term “circumference” is derived from the Latin word circumferre. This term was first used by Euclid in his work The Elements.