What’s the Deal with Pi Day on March 14?

On March 14 around the world, math teachers and math nerds get excited about Pi. They may even bring pies to school! Pi (or the Greek letter“π”) refers to the ratio of the circumference of a circle to its diameter. This number is 3.14159, but, actually, the number Pi has not been calculated completely. It’s an infinite number. But if we take the first three numbers, 3, 1, and 4, and find them on the calendar that’s March 14 – the fourteenth day of the third month. Started in the 1990’s, it’s become the most famous math-themed ‘holiday’.  

Knowing Pi, we can use this number to calculate the area of a circle or the volume of a sphere. Pi is used in dozens of mathematical formulas and physics calculations.

Here are a couple of ways you can learn more about Pi and why it’s important.

Celebrate Pi Day with a Book!

Sir Cumference and the Dragon of Pi (Overdrive eBook)

Sir Cumference is accidentally turned into a dragon, and his son must find the circumference of a circle to help him become a human again. This medieval and math themed series by Cindy Neuschwander and Wayne Geehan introduces math concepts in a picture book format. You’ll find six other Sir Cumference books in our Overdrive database.

Eat Your Math Homework by Ann McCallum

This book includes a chapter on Pi, as well as other math activities in the kitchen.

Learn about Pi Day online!

Pi Day | Celebrate Mathematics on March 14th – Learn about the history of Pi Day, how Pi is calculated and more on the official Pi Day website.

Circular Reasoning: Finding Pi | STEM Activity ( – In this hands-on activity you can measure three circles of different sizes and calculate Pi for yourself.