Pi Day 2025 is on Friday, March 14, 2025: Wtf is International Pi Day?

Friday, March 14, 2025 is Pi Day 2025. Pi day‎ March 14 is Pi Day 2014 Lesson Plans & Ideas for Teachers

Pi Day is an annual celebration commemorating the mathematical constant (pi). Pi Day is observed on March 14 (or 3/14 in the U.S.

3.141592653589793238462643383… That’s (a part of) the amount being celebrated on Pi Day! Pi (no, not cake) may be the relationship between your diameter and circumference of the circle, along with a mathematical constant.

Pi Day and Pi Approximation Day are two unofficial holidays held to celebrate the mathematical constant π (Pi). Pi Day is observed on March 14 (3/14 in American date format), due to π being equal to roughly 3.14. Sometimes it is celebrated on March 14 at 1:59 p.m. (commonly known as "Pi Minute"). If π is truncated to seven decimal places, it becomes 3.1415926, making March 14 at 1:59:26 p.m., "Pi Second". Pi Approximation Day may be observed on any of several dates, most often July 22 (22/7—in European date format—is a popular approximation of π). March 14 also happens to be Albert Einstein's birthday.

Why is march 14 known as pi day?

Pi Day and Pi Approximation Day are two unofficial holidays held to celebrate the mathematical constant π (Pi). Pi Day is observed on March 14 (3/14 in American date format, pi is approx 3.14); Pi Approximation Day may be observed on any of several dates, most often July 22 (22/7 - in European date format - is a popular approximation of π).

March 14 happens to be Albert Einstein's birthday, among others, and it is common to sing "Happy birthday Dear Albert". Massachusetts Institute of Technology often mails out its acceptance letters to be delivered to prospective students on Pi Day.

Some also enjoy celebrating "Pi Approximation Day" which can fall on any of several dates:

March 14 the approximation for Pi: 3.14

April 26 (when the distance of the Earth's orbit divided by the distance it has traveled so far is equal to pi; on leap years the 25th)[citation needed]

July 22 (22/7 in the majority of date formats, a popular approximation of pi)

November 10 (the 314th day of the year; on leap years the 9th)

December 21, 1:13 p.m. (the 355th day of the year (on leap years, the 20th), celebrated at 1:13 for the Chinese approximation 355/113)

What is this Pi Day?

Pi day is 3/14, because pi is approximately equal to 3.14.

Celebrating it or not is a personal choice, but it's one of the most important numbers in mathematics.

Pi is the circumference of a circle divided by its diameter.

Pi figures into a lot of circular functions in helping to find, for instance, surface area or volume of a sphere, or surface area or volume of a cylinder or donut-shaped tube. This is important when designing machines that manufacture such shapes. And because pi is an irrational number, which means it can be computed to an infinite number of decimals, this highly figures in to how accurate you want a machine to be made...for example, the wiring in computer chips which are really super-thin cylinders.

Pi has probably been noticed by someone since the first introduction of the Gregorian calendar.

It's also probably been celebrated by someone who has interest in math and just wants to do something. Celebrations don't all have to be big extravagant parties, it can be a simple as eating a slice.

Some teachers celebrate it by passing out slices of real pie or pizza. Non-math teachers can do this too if they like. Everything is entirely voluntary.

For more information on "bizarre and unique holidays", you can try here:

and just click "Bizarre and unique" on the left (Pi day is noted, too!)