What is Pi Day? The History of an Irrational Holiday

(Last Updated On: March 9, 2018)

 What is Pi Day?

What is Pi Day?

March 14th is Pi Day, an annual celebration of all things pi (π)!

In Mathematics, pi is a specific ratio – the circumference of a circle divided by its diameter. In other words, you can take the circumference of any sized circle, divide by its diameter, and you will always get pi. As a number, pi is irrational (meaning the decimal digits go on forever without a set pattern), but is commonly written as 3.14.

Yes, we have an entire day dedicated to a mathematical constant. What is Pi Day and how did such a holiday begin?

The first Pi Day is thought to have originated in 1988, when Larry Shaw, a physicist working at the San Francisco Exploratorium, organized events on March 14th of that year. The celebration included a circular parade and of course, lots of fruit pies.

Why was March 14th chosen as Pi Day? If you write the date out numerically, 3/14, it represents the first three digits of pi (3.14).

Like many other silly holidays, Pi Day festivities grew gradually over time, and were boosted with the help of the internet and social media. On March 12th, 2009, Pi Day became official. The US House of Representatives passed a non-binding resolution, making March 14th, 2009 National Pi Day.

Today, Pi Day continues to be a fun holiday recognized by many.

A History of Pi

Approximations of pi began centuries ago. Early Babylonian mathematicians noticed that the circumference of a circle was always around 3 times the diameter, regardless of what size the circle was. In the Old Testament (1 Kings 7:23), a circular pool is referred to as being 30 cubits around, and 10 cubits across.

In the 2nd century B.C., Greek mathematician Archimedes used polygons with many sides to approximate circles, and was able to calculate pi accurately to three decimal places. Fast forward nearly a millennium, and we see the Greek letter π used to represent pi for the first time by Welsh mathematician William Jones.  

Approximations of pi got more and more accurate over time, and today with the help of modern computers, pi has been calculated to over one trillion digits past its decimal! The infinite and patternless nature of pi make it a fun challenge to try and memorize. Thankfully, when computing math problems, the first three digits (3.14) or the fraction 22/7, are commonly used as accurate estimations.

Pi…What is it Good For?

Pi is closely related to the circle, and as such, is found in many fields of science and math. This is especially true for those that use circles, spheres, or ellipses, like statistics, physics, and engineering. However, you probably know pi from geometry or trigonometry class.

Do you remember how to find the area of a circle? For that, we use the equation:

A = πr²

Where ‘A’ is area, and ‘r’ is the radius (distance from the center to the edge of the circle).

How about the circumference of a circle? Remember, pi is the circumference of a circle divided by its diameter, so:


Where ‘C’ is circumference, and ‘d’ is diameter.

Okay, how about the volume of a cylinder? That would be:

V = πr²h

Where ‘V’ is volume, ‘r’ is radius, and ‘h’ is the height of the cylinder.

How to celebrate Pi Day

The best part about holidays like Pi Day is that you really can celebrate it however you want. Unlike the rest of math, there are no rules!

Since pi and pie are homophones in English, baking pies, eating pies, and throwing pies are all acceptable ways to celebrate. In fact, just about anything pie-related will work. However, pies are the only food you can eat. Anything circular will do just fine. Pizza anyone?

Know any fun math games? Pi Day is a great time to play them. Sporcle has tons of fun Math quizzes you can play as well! We recommend trying the Digits of Pi quiz.

Sporcle also has this nifty Pi Day badge you can earn – I like Pi.

At the end of the day, use this holiday to help get people interested in math and science. No idea is too irrational!

How do you plan to celebrate? Let us know in the comment section below.

About the Author:

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Mark Heald is the Managing Editor of Sporcle.com. He enjoys spending time with his family, traveling, and bemoaning the fact the Sonics left Seattle.