Calculating the circumference of a circle

The circumference of a circle is calculated using the formula below:

Circumference = 2 π r

Note: π is the symbol for pi (3.14) and r is the radius of the circle.

Example 1

The radius of a circle is 4 meters. What is the circumference of this circle?

Working

Circumference = 2 π r = 2 x 3.14 x 4 meters = 25.12 meters

Example 2

Keshann drew a circle with a radius of 6 cm. What is the circumference of that circle?

Working

Circumference = 2 π r = 2 x 3.14 x 6 cm = 37.68 cm

Note: The diameter of a circle is twice the length of the radius. Therefore the circumference of a circle can be calculated using the formula π d (pi x diameter)

Example 3

What is the circumference of a circle if its diameter is 18 feet?

Working

Circumference = π d = 3.14 x 18 feet = 56.52 feet