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*.