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Have A Slice of Pi

Original published date 3.9.2021. Updated 3.7.2023

March 14 is recognized in several countries around the world as Pi Day. It’s a celebration of that most famous transcendental number, π (pronounced pie), in which 3.14 are the first digits. In the United States, the designation of Pi Day started in 2009. Ten years later, the United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed March 14 as the International Day of Mathematics.

Pi is the ratio of a circle’s circumference to the diameter. Ancient civilizations like the Egyptians and Babylonians not only knew about the existence of pi, but also found its approximate values. We’re talking about 2000 B.C. here!

Standing on the shoulders of those civilizations, Archimedes created an algorithm to approximate π in 250 B.C. The earliest known use of the Greek letter π to represent the ratio is by Welsh mathematician William Jones in 1706, possibly as shorthand for the word, periphery.
Steven Bogart, a mathematics instructor at Georgia Perimeter College, provided this useful exercise in Scientific American:

“Using a compass, draw a circle. Take one piece of string and place it on top of the circle, exactly once around. Now straighten out the string; its length is called the circumference of the circle. Measure the circumference with a ruler. Next, measure the diameter of the circle, which is the length from any point on the circle straight through its center to another point on the opposite side. (The diameter is twice the radius, the length from any point on the circle to its center.) If you divide the circumference of the circle by the diameter, you will get approximately 3.14—no matter what size circle you drew!”

Pi is also an irrational number. So, what makes a number rational or irrational? John Urschel, mathematician and former Minnesota Vikings offensive lineman, provides a lecture on this subject as a part of the NMSI Free Lessons series.


So, what are your plans to commemorate Pi Day? Will pizza, pie or cookies be a part of the fun, along with our fun (and free) Pi Day Lessons? We believe every student deserves a piece of the Pi. Be sure to share your celebration with us by following NMSI on Twitter and Instagram and use the hashtags #PiDay #idm314 and #NMSINation.