Every year on March 14, math lovers around the country celebrate pi. Some enthusiasts even go so far as to mark Pi Minute at 1:59, which takes into account the first six digits of the pi: 3.14159. Pi Day provides the perfect excuse for incorporating math and geometry into all aspects of the school day.

### What Is Pi?

Pi is the circumference of a circle (the distance around the circle) divided by its diameter (the distance across). In other words, the circumference of any circle is approximately 3.14 times its diameter. Because pi is an irrational number, it has an infinite number of digits. No matter how many decimal places we calculate, pi will always be an approximation.

Because pi is the same for every circle, we can use it to determine the diameter if we know the circumference, or vice versa. And when we know the diameter, it’s easy to calculate the area.

This gif (animated sequence) that "unrolls" pi will give your students a quick visual of how a circle’s diameter, circumference, and pi are related.

### The History of Pi

From ancient China to Babylonia, mathematicians have been puzzling over pi for thousands of years. A Brief History of Pi explains the history of this fascinating number.

Since pi goes on forever, even the most powerful supercomputers will never know all of pi’s digits. But that doesn’t stop people from trying! In 2002, a team of mathematicians at the University of Tokyo broke the record, using computers to calculate pi to 1,241,100,000,000 decimal places. Check out this amazing display of the first million digits of pi.

### Fun With Pi

Pi gives ample opportunity for creative math fun. This amazing activity, for example, allows your students to play pi as a musical sequence! Simply pick ten notes, which are then assigned to integers, and then listen to what pi sounds like!

Your students can search pi for number combinations (birthdays, jersey numbers, lucky numbers) using the Pi Search Results Tool. It also allows you to view any section of pi in groups of 10 to 1000 digits.

Try Cutting Pi, a hands-on activity in which students measure cylindrical objects in the classroom with string, cut their measured string into three equal pieces, and then figure out how to measure the leftover piece. They'll see for themselves how pi comes up every time!

Learn how to make a circle from three points on a plane and have fun manipulating nested circles with this interactive tool that shows students that circles are awesome.

### For Younger Students

Introduce ideas such as size, shape, and circumference, among others, with Fun With Balls and Hoops, a physical development activity from Early Childhood Today.

Or take your kids into the kitchen to explore circumference, diameter, and fractions by making pizza pies with this activity plan from Early Childhood Today.

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