Pi Day

For National Pie Day, see American Pie Council.
Pi Day

Larry Shaw, the organizer of the first Pi Day celebration at the Exploratorium in San Francisco
Significance 3, 1, and 4 are the three most significant figures of π
Celebrations Pie eating, discussions about π[1]
Date March 14
Next time March 14, 2017 (2017-03-14)
Frequency annual
Related to Pi Approximation Day

Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (3/14 in the month/day date format) since 3, 1, and 4 are the first three significant digits of π.[2][3] In 2009, the United States House of Representatives supported the designation of Pi Day.[4]

Pi Approximation Day is observed on July 22 (22/7 in the day/month date format), since the fraction 227 is a common approximation of π, which is accurate to two decimal places and dates from Archimedes.[5]


The earliest known official or large-scale celebration of Pi Day was organized by Larry Shaw in 1988 at the San Francisco Exploratorium,[6] where Shaw worked as a physicist,[7] with staff and public marching around one of its circular spaces, then consuming fruit pies.[8] The Exploratorium continues to hold Pi Day celebrations.[9]

On March 12, 2009, the U.S. House of Representatives passed a non-binding resolution (HRES 224),[4] recognizing March 14, 2009 as National Pi Day.[10] For Pi Day 2010, Google presented a Google Doodle celebrating the holiday, with the word Google laid over images of circles and pi symbols.[11]

The entire month of March 2014 (3/14) was observed by some as "Pi Month".[12][13] In the year 2015, Pi Day had special significance on 3/14/15 (mm/dd/yy date format) at 9:26:53 a.m. and also at p.m., with the date and time representing the first 10 digits of π.[14] Pi Day of 2016 is also significant because its mm/dd/yy represents pi rounded to the first five digits.


Pi Day has been observed in many ways, including eating pie, throwing pies and discussing the significance of the number π, due to a pun based on the words "pi" and "pie" being homophones in English (pronunciation: /p/).[1]

Massachusetts Institute of Technology has often mailed its application decision letters to prospective students for delivery on Pi Day.[15] Starting in 2012, MIT has announced it will post those decisions (privately) online on Pi Day at exactly 6:28 pm, which they have called "Tau Time", to honor the rival numbers pi and tau equally.[16][17] In 2015, the regular decisions were put online at 9:26 AM, following that year's "pi moment".[18]

The town of Princeton, New Jersey, hosts numerous events in a combined celebration of Pi Day and Albert Einstein's birthday, which is also March 14.[19] Einstein lived in Princeton for more than twenty years while working at the Institute for Advanced Study. In addition to pie eating and recitation contests, there is an annual Einstein look-alike contest.[20]

See also


  1. 1 2 Landau, Elizabeth (2010-03-12). "On Pi Day, one number 'reeks of mystery'", CNN. Retrieved on 2010-03-14 from http://www.cnn.com/2010/TECH/03/12/pi.day.math/index.html.
  2. Bellos, Alex (March 14, 2015). "Pi Day 2015: a sweet treat for maths fans". theguardian.com. Retrieved March 14, 2016.
  3. Program on Sveriges Radio - Swedish national radio company Read 2015-03-14
  4. 1 2 United States. Cong. House. Supporting the designation of Pi Day, and for other purposes. 111th Cong. Library of Congress.
  5. "Pi Approximation Day is celebrated today.". Today In History. Verizon Foundation. Retrieved 2011-01-30.
  6. Berton, Justin (March 11, 2009). "Any way you slice it, pi's transcendental". San Francisco Chronicle. Retrieved 2011-03-18.
  7. Jonathan Borwein (10 March 2011). "The infinite appeal of pi". Australian Broadcasting Corporation. Retrieved 2011-03-13.
  8. Adrian Apollo (March 10, 2007). "A place where learning pi is a piece of cake" (PDF). The Fresno Bee.
  9. "Exploratorium 22nd Annual Pi Day". Exploratorium. Retrieved 2011-01-31.
  10. McCullagh, Declan (March 11, 2009). "National Pi Day? Congress makes it official". Politics and Law. CNET News. Retrieved 2009-03-14.
  11. "Pi Day". Google Doodles. Google. Retrieved 2012-10-09.
  12. By Douglas Main (2014-03-14). "It's Not Just Pi Day, It's Pi Month! | Popular Science". Popsci.com. Retrieved 2014-07-22.
  13. "Pi Month Celebration & Circle of Discovery Award Presentation | College of Computer, Mathematical, and Natural Sciences". Cmns.umd.edu. 2014-03-11. Retrieved 2014-07-22.
  14. Ro, Sam (March 13, 2014). "March 14, 2015 Will Be A Once-In-A-Century Thrill For Math Geeks". Business Insider. Retrieved 13 March 2014.
  15. McClan, Erin (March 14, 2007). "Pi fans meet March 14 (3.14, get it?)". msnbc.com. Retrieved 2008-01-24.
  16. "I have SMASHING news!". MIT Admissions. Retrieved 2012-03-12.
  17. McGann, Matt. "Pi Day, Tau Time". MIT Admissions. Retrieved 2012-03-18.
  18. http://mitadmissions.org/blogs/entry/keep-your-eyes-to-the-skies
  19. "Princeton Pi Day & Einstein Birthday Party". Princeton Regional Convention and Visitors Bureau. Retrieved 2012-12-27.
  20. "Princeton Pi Day & Einstein Birthday Party". Princeton Regional Convention and Visitors Bureau. Retrieved 2013-03-14.
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