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Pi Day is coming up next week on March 14 (3/14), chosen because the first three digits of pi are 3.14... It is a fun way to celebrate the mathematical constant π and all things math.

Pi is based on the relationship (ratio) between circumference of a circle and its diameter. If you're a bit rusty in math, the diameter is a straight line segment that passes through the center of a circle and has endpoints on the circle. The circumference is the distance around the outside of the circle.

Public domain image by Kjoonlee, based on previous work by w:User:Papeschr at  Wikimedia

Pi was first established as the ratio of the circumference to the diameter.

π = C/d

It is a fascinating number because it is so useful, but it is also irrational. That means it is an infinite, non-repeating decimal.

Pi Day activities can run the gamut from serious to seriously lighthearted.

Public domain image of a Pi Day pie

You might want to check out

One great way to celebrate Pi Day is to read a book about math. We maintain a list of children's math books for Pi Day and every day at Science Books for Kids. Let's add some recent releases to the list:

Goodnight, Numbers by Danica McKellar and illustrated by Alicia Padron is for children who are learning their numbers.

Danica McKellar is not just another celebrity using their fame to hawk children's books. She is a serious mathematician whose goal is to get kids excited about math through books and videos. Her first books were for middle and high school aged kids. Now she's writing for the youngest set.

You can see what she has to say in this book trailer:

Age Range: 2 - 5 years
Publisher: Crown Books for Young Readers (March 7, 2017)
ISBN-10: 110193378X
ISBN-13: 978-1101933787

STEAM stands for science, technology, engineering, art, and math.  This is Not Another Math Book by Anna Weltman and ilustrated by‎ Charlotte Milner is a perfect choice for older kids who want to explore art as a way to understand math.

Author Anna Weltman has created an imaginative series of hands-on projects that include exploring symmetry by drawing kaleidoscopic patterns, growing a forest of fractal trees, and assembling five-square pentomino shapes into pictures.

Ages: 9+
Paperback: 96 pages
Publisher: Kane Miller Books / EDC Publishing; First American edition (2018)
ISBN-10: 1610675975
ISBN-13: 978-1610675970

For the full list, see children's math books for Pi Day and every day at Science Books for Kids.


What is Pi Day?

Pi Day has been celebrated each year on March 14 (3/14) as a fun salute to pi = 3.14...  This year, Pi Day will have special significance because 3/14/15 at 9:26:53 a.m. and p.m. will represent the first 10 digits of pi. Plus, March 14 happens to be Albert Einstein's birthday. Cool!


What is Pi?

Pi is is the ratio between the circumference (distance around a circle), and the diameter (the distance across the circle). It written as p in Greek alphabet, which is the symbol π. Pi is an infinite decimal with a value 3.14159265358979323846…

Want more details? SciShow has an explanation of pi useful for older students.

Activities for Pi Day:



1. Baking

It has become somewhat of a tradition to bake a pie to share for Pi Day with a π symbol on it. Another option would be to make π pancakes. See how to make them at Pi Day Pancakes  (Your Individual Taste).

2. Toothpick Toss

One way to calculate pi involves comparing the circumference of a circle to the diameter. Another way is to count how many toothpicks (or other similar objects) fall in a certain way when thrown at a series of parallel lines.


  • Toothpicks (matchsticks also work) - at least 100
  • Cardboard or poster board surface to draw lines on
  • Ruler
  • Marker (such as Sharpie)
  • Calculator (optional)

Draw several parallel lines on the cardboard or poster board with the distance between each line exactly equal to the twice the length of a toothpick. Randomly toss toothpicks onto the lined surface, keeping track of the total number of toothpicks tossed. When you are done, count each toothpick that has landed crossing a line in any way. 

Divide the total number of toothpicks tossed by the number of toothpicks that crossed the lines. See how close to pi your estimate is.

For more details and slightly different methods, check Estimating pi by dropping sticks (with a simulation to try) at SciFriday. Exploratorium also has a discussion the toothpick toss and other Pi Day Activities.

3. Read a Pi Day Book

Sir Cumference and the Dragon of Pi (A Math Adventure)
by Cindy Neuschwander and illustrated by Wayne Geehan

Meet the regulars in King Arthur’s court, such as Sir Cumference, his wife Lady Di of Ameter, their son Radius, and the carpenter, Geo of Metry. When Sir Cumference turns into a dragon, can his family and friends use math to save him? Although it looks a bit like a picture book, the concepts are actually for middle grades.

This video shows a reading of the book.

For more book suggestions, check the list of Math Books for Pi Day and Every Day at Science Books for Kids.


Want more? There's a plethora of links to all things pi at Joy of Pi.


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