In the work, the term "circumference" is used to mean the perimeter of a circle.

However, some authors allow "circumference" to refer more generally to the distance or arc length around an arbitrary closed object (sometimes restricted to a closed plane figure such as a lamina).

For a circle with radius and diameter ,

where is pi.

The term "circumference" has a special meaning when referring to a graph circumference.

Half of the circumference is sometimes (especially in older literature) referred to as the semicircumference.