Pi Day 2027 is on Sunday

About Pi Day

Pi, written with the Greek letter π, is what you get when you divide the distance around any circle by the distance across it. It begins 3.14159, and because pi is an irrational number its decimal digits go on forever without falling into a repeating pattern. Pi Day turns that idea into a party. Classes measure round objects to estimate pi, students compete to recite as many digits as they can, and plenty of people eat pie for the pun.

The day started in 1988 at the Exploratorium, the hands-on science museum in San Francisco. According to the museum, staff physicist Larry Shaw connected March 14, or 3.14, with pi's opening digits during a staff retreat that year. The first celebration was modest: Shaw and his wife, Catherine, set out fruit pies and a tea urn on the museum floor at 1:59, the digits that follow 3.14. Shaw, known around the museum as the Prince of Pi, led its Pi Day parade every year until his death in 2017. The Exploratorium still holds a public celebration that includes a procession circling its Pi Shrine 3.14 times. The date is also Albert Einstein's birthday, a coincidence the museum likes to point out.

On March 12, 2009, the US House of Representatives passed House Resolution 224 by a vote of 391 to 10. The resolution supported the designation of Pi Day and encouraged schools and teachers to use it to get students interested in math, but it was a nonbinding statement and did not create a federal holiday. A decade later the date gained a second, global role: on November 26, 2019, UNESCO's General Conference proclaimed March 14 the International Day of Mathematics. Led by the International Mathematical Union, that day was first celebrated in 2020 and covers all of mathematics, with a new theme each year.

Sources: Exploratorium: A Slice of Pi Day History, Exploratorium: Pi Day, Congress.gov: H.Res.224, 111th Congress (2009), House Committee on Science and Technology: House encourages students to observe Pi Day (2009), International Day of Mathematics: About, UNESCO: International Day of Mathematics. How we check dates.

How to mark Pi Day

• Measure the circumference and diameter of round things at home, such as cans, plates and bike wheels, then divide one by the other to see how close you get to 3.14.
• Estimate pi by chance: drop toothpicks onto paper ruled with lines one toothpick-length apart, then divide twice the number of tosses by the number that land across a line.
• Write a "piem," a short poem in which the number of letters in each word matches the digits of pi in order (3, 1, 4, 1, 5 and so on).
• Share a pie and cut it into equal slices to talk about angles, fractions and why the slices meet at the center.
• Look up the International Day of Mathematics theme for the year and join a school, library or online activity built around it.

Pi Day dates