Pi, a mathematical constant denoted by the Greek letter π, is the ratio of a circle's circumference C to its diameter d: π = C/d. The circumference of a circle is, in turn, equal to 2πr, where r is ...

Introduction If you wanted to measure the circumference of Earth, how long would your tape measure have to be? Would you need to walk the whole way around the world to find the answer? Do you think ...

People across the world are eating pies and celebrating the circle this Saturday — and this year's Pi Day is particularly special. The full date, 3/14/15, is pi to the first four places. At 9:26 a.m.