Do you have March 14 circled on your calendar? If you do, then you’ve probably been looking forward to the annual celebration of Pi Day, when we recognize the mathematical constant pi (π). Approximated as 3.14, pi is the ratio of the circumference to the diameter of a circle. Public observations often include marching in a circle, eating pie, or reciting as many digits of pi as possible (3.1415926535…).
While March 14 is the day on which pi is observed around the world, this useful number can also be honored on other days. Read on to learn about more ways to celebrate pi.
January 11 – Pi Percent Day: Mid-day on January 11 marks the point when 3.14% of the year will have passed. That’s a really small slice. If only we kept our holiday dessert slices this small – we just might have fewer extra pounds to shed. | |
April 4 – Pi Day by Months: 3.14 months of the year will have passed on April 4, making it another opportunity to commemorate the mathematical constant pi. | |
June 28 – Two-Pi Day: If we use the ratio of any circle’s circumference to its radius (rather than its diameter), we get 6.28, or twice the value of pi. The combination 2π occurs frequently throughout mathematics, and it has been defined as t (tau). | |
July 22 – Pi Approximation Day: The fraction 22/7 is often used as an approximation of pi, since the first few digits of the fraction are 3.142857 – pretty close. July 22 is also known as European Pi Day, since many in the region write dates in the day/month format. | |
November 10 – 314th Day of the Year: Perhaps one of the most straight-forward days to observe the first few digits of pi is on November 10. That’s the 314th day of the year (except in leap years, when it is November 9). |
If you are looking for still more days to celebrate, we’ve pulled together a list of some additional fun math dates.
February 7 – e Day: Commemorates the mathematical constant e (2.7182818), also called Euler’s Number after the Swiss mathematician Leonhard Euler. It is the base of the natural logarithm and, along with pi and others, is one of the most important numbers in mathematics. | |
August 15, 2017 – Pythagorean Theorem Day: The date observing the Pythagorean Theorem (a^{2} + b^{2} = c^{2} for right triangles) varies depending on when the values for the month, day, and year form a right triangle. This year, 8/15/17 fits the calculation. | |
October 23 – Mole Day: The Avogadro constant (~6.02 x 10^{23} mol^{-1}) can be celebrated from 6:02 a.m. to 6:02 p.m. on 10/23. This basic unit of measure in chemistry describes the number of atoms or particles in a “mole” of a substance; hence, the nickname “Mole Day.” | |
November 23 – Fibonacci Day: The Fibonacci sequence is generated by adding the previous two numbers (after the first two). The beginning of the sequence 1, 1, 2, 3, 5, 8, 13… can be written in date form as 11/23, or November 23. | |
May 5, 2025 – Square Root Day: Square root days occur when both the day and the month are the square root of the last two digits of the year. There are only nine of these each century and the next one will occur on 5/5/25. It’s not too early to start planning your celebration! |