What Is Pi Day?

Pi DayA group of middle school students forming the Greek letter π in honor of Pi Day. The holiday, a time to celebrate the number pi (which is about 3.14) and math in general, occurs each year on March 14 (or 3/14).

Pi Day is a celebration of the never-ending mathematical constant pi (π), which relates the circumference C of a circle to its diameter d; that is, π = C/d.The numerical value of pi to five decimal places is 3.14159; hence, Pi Day is celebrated on March 14 (3/14).

Pi Day is often celebrated with pies or pizzas decorated with the Greek letter π. American physicist Larry Shaw, who worked at the Exploratorium, a science museum in San Francisco, devised the holiday at a staff retreat in 1988. The first Pi Day celebration began that March 14 at 1:59 pm (following the next digits in pi after 3.14).

Ways to Celebrate Pi Day
  • Eat some pie.
  • See how many digits of pi you can memorize.
  • Run 3.14 miles (or kilometers).
  • Admire pi in nature.

Several years after the first Pi Day, Shaw’s daughter, Sara, noticed that the day was also Albert Einstein’s birthday (March 14, 1879), and it has thus become a celebration of both science and mathematics. In 2019 the United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed March 14 the International Day of Mathematics because of the widespread celebration of Pi Day.

Erik Gregersen
Citation Information
Article Title: What Is Pi Day?
Website Name: Encyclopaedia Britannica
Publisher: Encyclopaedia Britannica, Inc.
Date Published: 25 August 2026
Access Date: November 13, 2026