# What is pi?

For any circle, $$circumference \div diameter = 3.141592...$$

This number is so special that it is given its own symbol $$\pi$$ (the Greek letter pi).
The value $$\pi$$ is a constant, but is called an as an exact value for $$\pi$$ does not exist. In non-calculator working out, approximate values are used, of which $$3.14$$ and $$3.142$$ are probably the most common. Other, less accurate approximations are $$\frac{22}{7}$$ and $$3$$.
All scientific calculators have a $$\pi$$ button. You can use this to make your calculations more accurate.
The earliest known use of the Greek letter $$\pi$$, to represent the ratio of a circle's to its diameter, was by the Welsh mathematician William Jones in his 1706 work ‘Synopsis Palmariorum Matheseos’ or, ‘A New Introduction to the Mathematics’.