Circles are 2D shapes with one side and no corners. The circumference is always the same distance from the centre - the radius. Sectors, segments, arcs and chords are different parts of a circle.

Part of

The **circumference** of a circle is the distance around the circle. It is another name for the **perimeter** of a circle.

The circumference of a circle is calculated using the formula:

For any circle:

This number is **Pi**. It is a number which goes on forever.

The pi symbol ( ) allows you to give the exact value to a calculation involving circles as pi cannot be written as an exact fraction or decimal. If a decimal answer is required, the value can be approximated as 3.14 (3 significant figures).

Scientific calculators have a button which can be used during calculations, with the final answer being rounded off as appropriate.

Calculate the circumference of the dartboard.

The diameter is twice the radius.

Circumference = (1 decimal place).

The answer can also be given in terms of . In this case the answer is .

The circumference formula can be used to solve problems.

- Question
How many full rotations will the wheel make if it travels 3,500 cm?

Circumference of the wheel is: (1 decimal place)

In one rotation the wheel travels 172.8 cm (or 55 ).

To calculate the number of rotations:

(or

This is 20 full rotations.

In this case, rounding off early did not change the final answer. For the most accurate answer you should avoid rounding off until the end if possible.