Calculating the ratio of a circle's circumference to its diameter is as easy as pi.

Today is Pi Day, an event that celebrates this mathematical constant.

This date was chosen because 3, 1, and 4 are the first three significant figures of pi (π) when it is written out.

Pi is an irrational number, which means that it can't be written as a fraction.

When written out, its decimal representation goes on infinitely without repeating.

The oldest attempts to calculate pi date back to ancient Babylon and Egypt, around 1900 BCE.