What is pi?

• Pi, or π, is a number that is used to represent the ratio between a circle's circumference and its diameter.

• The value of pi is always the same no matter how big the circle is.

• Its actual value is slightly bigger than 3, but we tend to just use 3 to make calculations easier.

Pi is used in every formula where we are trying to work out the size or shape of a circular object. For example:

• circumference of circle = πd

• area of a circle = πr²

• surface area of sphere = 4πr²

• volume of sphere = ⁴⁄₃πr³