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 = π
area of a circle = π²
surface area of sphere = 4π²
volume of sphere = ⁴⁄₃϶ݳ
More on Shape, space and measures
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