# Measure of a Circle

## Measure of a Circle

Number, called the circumference, that expresses the length of a circle.

### Formula

The formula to calculate the circumference of a circle is: C = 2πr = πd.

### Examples

• This circle has a radius of 3 centimetres.

C = 2πr
C ≈ 2 × 3.1416 × 3
C ≈ 18.8496 cm

• The circumference of the Earth is approximately 40 000 km.