National Pi Day is observed annually on March 14 in the United States, a date that corresponds to the first three digits of the mathematical constant π (3.14). The holiday marks the occasion with events, competitions, and the eating of pie, and is one of the few national days to have received formal recognition from Congress, designated as such by the House of Representatives in 2009.
What Is Pi?
Pi (π) is the ratio of a circle’s circumference to its diameter — the result of dividing how far around a circle is by how wide it is. This ratio is the same for every circle, regardless of size, and equals approximately 3.14159.
Pi is classified as an irrational number, meaning its decimal expansion has no end and no repeating pattern. It has been calculated by computer to trillions of decimal places, and no pattern has been found.
How Did Pi Day Start?
Pi Day was first celebrated in 1988 at the Exploratorium science museum in San Francisco, organized by physicist Larry Shaw. The event consisted of a march around one of the museum’s circular spaces followed by the eating of fruit pies. The Exploratorium continues to hold Pi Day events annually.
In 2009, the US House of Representatives passed a resolution recognizing March 14 as National Pi Day.
🧮 In 2019, UNESCO designated the date the International Day of Mathematics. March 14 is also the birthday of Albert Einstein.
How Do People Celebrate?
The most popular tradition is simply eating pie — the wordplay is too good to resist. Pizzerias and bakeries often offer Pi Day discounts. Schools hold competitions to see who can recite the most decimal places of pi from memory. Some universities, like MIT, have historically tied important announcements to the date.
Princeton, New Jersey throws a particularly enthusiastic celebration, since March 14 is also Albert Einstein’s birthday (he lived and worked there for over twenty years). Events include pie-eating contests, pi recitation, and an Einstein look-alike competition.
In 2024, recreational mathematician Matt Parker led a team of hundreds of volunteers in calculating 139 digits of pi entirely by hand over six days — claimed to be the largest such hand calculation in a century.
Pi Day in the United States
In the U.S., Pi Day is especially popular in schools and universities. Teachers often use it as a chance to approach math creatively, through games, challenges, and real-world examples rather than formulas alone.
Outside classrooms, the day has taken on a lighter tone. Bakeries promote pie, workplaces run low-key math trivia, and social media fills with jokes that mix numbers and dessert. The balance of learning and fun is what keeps the day widely appealing.
