What is Pi Day?


  • March 14 is Pi Day, a celebration of the beloved constant pi. This year, however, not many are celebrating, with the coronavirus outbreak having restricted public gatherings.

What is Pi Day?

  • It is dedicated to pi, whose value up to five decimal places is 3.14159. The idea originated in the United States, where the convention is to write dates in a format that expresses March 14 as 3/14. These three digits match the value of pi up to two decimal places, at 3.14. Coincidentally, March 14 is also Albert Einstein’s birthday.
  • The late Larry Shaw, a physicist with the Exploratorium museum in San Francisco, came up with the idea of Pi Day in 1988. The Exploratorium launched celebrations on 3/14, at 1:59, to correspond with 3.14159. The Exploratorium tradition eventually spread across the world among mathematicians, scientists and ordinary fans of pi.
  • In 2009, the US House of Representatives adopted a resolution supporting the designation of Pi Day and its celebration around the world. The House “encourages schools and educators to observe the day with appropriate activities that teach students about Pi and engage them about the study of mathematics”, the resolution said.

But why pi, in particular?

  • Vital to a wide range of calculations, pi is also the most familiar of all mathematical constants. The concept is introduced to schoolchildren when they are taught to calculate the area and circumference of a circle. They usually work with the fraction 22/7, which gives an approximate value for pi.
  • By definition, pi is the ratio of the circumference of a circle — any circle — to its diameter. It is remarkable because the ratio is always constant. Pi is also the area of a circle divided by the square of its radius — again a constant ratio for any circle. This was something that caught the attention of ancient mathematicians; the Babylonians took the ratio as 3. Centuries of observations and calculations have refined the value of pi, with modern computers having gone up to trillions of digits (digits after the decimal continue forever, for pi is an “irrational number”.)
  • Besides being indispensable in geometry and by extension trigonometry, pi has applications in physics, astronomy and other sciences, and appears in various formulas.

What happens on Pi Day?

  • At an institutional level, the Americans take the lead. The Exploratorium organises multiple activities relating to pi, including methods for calculating its value and a “Pi procession”, and invites fans across the world to do the same. The Massachusetts Institute of Technology announces its admission decisions for the next batch on Pi Day. NASA, which has a dedicated Pi Day page on its website, says its celebrates Pi Day everyday by using pi to explore space.
  • Outside the US, various universities report every year how they celebrated Pi Day. The Indian Institute of Science Research and Education (Pune), for instance, described in 2015 how it launched its pi-related activities on 3-14-15 at 9.26 am (pi = 3.1415926…).
  • Many non-Americans find it difficult to associate pi with March 14, which they express as 14/3 rather than 3/14. Other dissenters have noted that we usually work with a circle’s radius, not its diameter. The ratio of a circle’s circumference to its radius, they point out, is 2 times pi, or 6.28. Therefore, they prefer to celebrate on 6/28 (June 28), which they call “Tau Day”.

What’s different this year?

  • Because of the outbreak, public events are mostly off. The Exploratorium, which has shut until the end of March, announced that Pi Day celebrations are postponed. A number of universities, too, have announced postponement of Pi Day events.
  • Fans often celebrate Pi Day with a pie, which rhymes with pi, is circular, and lends itself to pi-related activities. Bakeries usually see a boom in sales in the days leading up to Pi Day, but this year they are missing that bump, CNBC reported, describing trends in San Francisco, New York and Seattle.


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