Every year on March 14 math lovers around the country celebrate pi, the irrational number commonly abbreviated to 3.14. Some enthusiasts go so far as to mark Pi Minute, 1:59 PM, taking into account the first six digits of the number: 3.14159.
Start your math festivities with a hands-on activity. With Discovering Pi (PDF), your students can measure cylindrical objects in the classroom and then see for themselves how pi comes up every time.
What Is Pi and How Do We Use It?
Pi is the number you get when you divide the circumference of a circle (the distance around the circle) 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. When we know the diameter, it’s easy to calculate the area.
Show your students exactly how a circle’s diameter, its circumference, and pi are related with this short animated sequence.
Then play The Story of Pi, a computer animated video from Project MATHEMATICS! that uses dynamic illustrations and straightforward narration to explain exactly what pi is and why it’s important.
The History of Pi
People have been searching for pi for thousands of years — at least since the ancient Babylonians discovered it 4,000 years ago. To find out how mathematicians have puzzled over this problem, read “A Brief History of Pi.”
Since pi goes on forever, even the most powerful supercomputers can never know all of pi’s numbers. That doesn’t stop people from trying, however. 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. You can see the first million here.
Fun With Pi
Pi’s very length suggests creative math fun. On this site, your students can assign a musical note to each number — and then play their own version of pi!
You can also have your students search pi’s digits for their birthdays or other number combinations using the Pi Search Results Tool .
More Activities With Circles and Pi(es)
Pi Day provides the perfect excuse for incorporating math and geometry into all aspects of the school day. Celebrate circles, math, and pi’s yummiest homophone with these hands-on activities!
Fun With Balls & Hoops – Introduce the concept of circumference and other math and science topics using this Early Childhood Today physical development activity.
Making a Pizza Pie – Develop students' math, science, and literacy skills by learning how to prepare a pizza in this ready-to-use lesson for mixed ages.
For Grades 2 and Up
Circles Are Awesome – Learn how almost any three points on a plane create a circle and then make your own kaleidoscopic art with nested circles.
We Love Math! – Pose challenging questions to involve students in using multiple skills to solve math problems. This Instructor Magazine article discusses open-ended questions as well as picture book, group, and everyday math.
Peering Into Pie Charts Lesson Plan Grades 4–6 – Understand how to use and critically read pie charts.
Interpreting Pie Charts Lesson Plan Grades 6–8 – Use pie charts in this real world math activity, in which students discuss rising gas prices and see how they affect a vacation budget.
And don’t forget that Pi Day is also Albert Einstein’s birthday. Visit the American Museum of Natural History’s kids’ page, Way to Go, Einstein!, to learn about the famed mathematician and physicist and to explore space and light.