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.

The letter C represents the circumference of the circle.
The letter r represents the radius of the circle.
The letter d represents the diameter of the circle.
The value of π is approximately 3.1416.

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.