Pi Day

Pi Day falls on March 14 each year, a date chosen because 3/14 mirrors 3.14 — the first three digits of π, the ratio of a circle’s circumference to its diameter. What began as a small gathering at a science museum has grown into an international nod to mathematics, marked by pie, digit-reciting contests, and hands-on classroom experiments.

The origins of Pi Day

In 1988, physicist Larry Shaw organized the first Pi Day at the Exploratorium, the science museum in San Francisco where he worked. Staff and visitors marched in a circle and then ate fruit pies — a pun on “pi” and “pie” that has defined the day ever since. Shaw, later nicknamed the “Prince of Pi,” turned it into an annual tradition. The idea spread through schools and universities, and in 2009 the U.S. House of Representatives passed a resolution recognizing March 14 as National Pi Day. A decade later, in 2019, UNESCO designated the same date as the International Day of Mathematics, giving the celebration a global, official footing.

The date carries other coincidences. March 14 is Albert Einstein’s birthday — he was born in 1879 — and it is also the day physicist Stephen Hawking died, in 2018.

How Pi Day is observed

The most common tradition is simply eating pie, whether sweet, savory, or a literal pizza pie, often cut to show off its circular shape. Schools and museums host pi-reciting contests, where participants recall as many digits as they can; the Guinness-recognized record belongs to Rajveer Meena of India, who recited 70,000 digits in 2015. Some enthusiasts time the moment to 1:59, extending the date to 3.14159.

Because π is irrational, its decimal expansion never ends and never repeats, which makes the number a natural centerpiece for math outreach — circle-measuring experiments, puzzles, and pi-themed runs of 3.14 miles. For those who prefer fractions, there is even a companion date: Pi Approximation Day on July 22, since 22/7 is a close approximation of pi.