## The Lesson

The circumference is the distance measured around a circle. The circumference is often denoted by C. The image below shows what we mean by the circumference:

## Dictionary Definition

The Oxford English Dictionary defines the circumference as "the curved line which forms the boundary of a circle."

## Examples of the Circumference

The circle below has a circumference of 20 cm. This is the distance around the circle.

The circle below has a circumference of 12 inches.

## How to Find the Circumference

The circumference of a circle is related to its radius and diameter.

## How to Find the Circumference from the Radius

The circumference is the radius multiplied by 2π. If the circumference is C and the radius is r (as shown in the image below), then we can find the circumference using the formula:

## How to Find the Circumference from the Diameter

The circumference is the diameter multiplied by π. If the circumference is C and the diameter is d (as shown in the image below), then we can find the circumference using the formula: