# Circumference and arc length

**The value of ***π*

*π*

For any circle the circumference is always just over three times bigger than the diameter which is also called π (pi).

An approximation of π is also 3.14 or 22/7.

**The circumference of a circle**

For any circle, π = circumference (C) / diameter (*d*)

For example, use π = 3.14 to find the circumference of a circle:

C = π*d*, where *d *9.5 cm

C = 3.14 x 9.5

C = 28.83 cm

**Finding the circumference given the radius**

The diameter of a circle is two times its radius therefore this is represented as followed:

*d* = 2*r*

**Finding the radius given the circumference**

The following formula is used to find he radius of a circle with the given circumference:

*C* = 2π*r*

**Finding the length of an arc**

The length of an arc of a given section from a circle is calculated using the following formula:

Arc length AB = (2π*rθ* / 360) x (π*rθ /* 180)