Geometry

Remember:

\[Radius = \frac{1}{2}diameter\]

\[Diameter = 2 \times radius\]

Diagram of a circle with arrows detailing the circumference, radius and diameter

Circumference of a circle

For any circle with a diameter, d, the circumference, C, is found by using the formula:

\[C = \pi d\]

where \(\pi = 3.14\)

Question

Calculate the circumference of the circle shown below.

Diagram of a circle with a diameter of 20cm

\[C = \pi d\]

\[= 3.14 \times 20\]

\[= 62.8cm\]

Question

Calculate the circumference of the circle shown below.

Diagram of a circle with a radius of 12cm

As you can see from the diagram, the radius is 12 cm.

Remember \(Diameter = 2 \times radius\)

\[Diameter = 2 \times 12 = 24cm\]

\[C = \pi d\]

\[= 3.14 \times 24\]

\[= 75.36cm\]