Pi Day

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Pi Day
Larry Shaw, the organizer of the first Pi Day celebration at the Exploratorium in San Francisco
Observed byUnited States
Significance3, 1, and 4 are the three most significant figures of π in its decimal representation.
CelebrationsPie eating, pi memorization competitions, discussions about π[1]
DateMarch 14
Next timeMarch 14, 2025 (2025-03-14)
First time1988
Related toPi Approximation Day

Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (the 3rd month) since 3, 1, and 4 are the first three significant figures of π, and it was first celebrated in the United States.[2][3] It was founded in 1988 by Larry Shaw, an employee of the San Francisco science museum, the Exploratorium. Celebrations often involve eating pie or holding pi recitation competitions. In 2009, the United States House of Representatives supported the designation of Pi Day.[4] UNESCO's 40th General Conference designated Pi Day as the International Day of Mathematics in November 2019.[5][6]

Other dates when people celebrate pi include Pi Approximation Day on July 22 (22/7 in the day/month format, an approximation of π) and June 28 (6.28, an approximation of 2π or tau).


In 1988, the earliest known official or large-scale celebration of Pi Day was organized by Larry Shaw at the San Francisco Exploratorium,[7] where Shaw worked as a physicist,[8] with staff and public marching around one of its circular spaces, then consuming fruit pies.[9] The Exploratorium continues to hold Pi Day celebrations.[10]

On March 12, 2009, the U.S. House of Representatives passed a non-binding resolution (111 H. Res. 224),[4] recognizing March 14, 2009, as National Pi Day.[11] For Pi Day 2010, Google presented a Google Doodle celebrating the holiday, with the word Google laid over images of circles and pi symbols;[12] and for the 30th anniversary in 2018, it was a Dominique Ansel pie with the circumference divided by its diameter.[13] In Indonesia, as a country that uses the DD/MM/YYYY date format, some people celebrate Pi Day every July 22, referring to another Pi number, namely 22/7.[14]

Some observed the entire month of March 2014 (3/14) as "Pi Month".[15][16] In the year 2015, March 14 was celebrated as "Super Pi Day".[17] It had special significance, as the date is written as 3/14/15 in month/day/year format. At 9:26:53, the date and time together represented the first ten digits of π,[18] and later that second, "Pi Instant" represented all of π's digits.[19]


Pi Day related offering at Delicious Orchards, a country food market in Colts Neck, New Jersey

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 ( /p/), and the coincidental circular shape of many pies.[1][20] Many pizza and pie restaurants offer discounts, deals, and free products on Pi Day.[21] Also, some schools hold competitions as to which student can recall pi to the highest number of decimal places.[22][23]

The Massachusetts Institute of Technology has often mailed its application decision letters to prospective students for delivery on Pi Day.[24] 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.[25][26] In 2015, the regular decisions were put online at 9:26 am, following that year's "pi minute",[27] and in 2020, regular decisions were released at 1:59 pm, making the first six digits of pi.[28]

Princeton, New Jersey, hosts numerous events in a combined celebration of Pi Day and Albert Einstein's birthday, which is also March 14.[29] 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.[29]

Alternative dates[edit]

Pi Approximation Day is often observed on July 22 (22/7), though this circle is not perfect at illustrating pi.

Pi Day is frequently observed on March 14 (3/14 in the month/day date format), but related celebrations have been held on alternative dates.

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.[30]

Two Pi Day, also known as Tau Day, is observed on June 28 (6/28 in the month/day format).[31] 2π, also known by the Greek letter tau (𝜏), is a common multiple in mathematical formulae and approximates to 6.28. Some have argued that 𝜏 is the more fundamental constant and that Tau Day should be celebrated instead.[32][33][34] Celebrations of this date jokingly suggest eating "twice the pie".[35][36][37]

Some also celebrate pi on November 10, since it is the 314th day of the year.[38]


See also[edit]


  1. ^ a b Landau, Elizabeth (March 12, 2010). "On Pi Day, one number 'reeks of mystery'". CNN. Retrieved March 14, 2018.
  2. ^ Bellos, Alex (March 14, 2015). "Pi Day 2015: a sweet treat for maths fans". theguardian.com. Retrieved March 14, 2016.
  3. ^ "Nedräkning mot internationella Pi-dagen". Swedish national radio company (in Swedish). March 14, 2015.
  4. ^ a b United States. Cong. House. Supporting the designation of Pi Day, and for other purposes. 111th Cong. Library of Congress Archived August 7, 2009, at the Wayback Machine
  5. ^ "International Day of Mathematics". UNESCO. March 4, 2020.
  6. ^ Rousseau, Christiane (September 1, 2019). "International Day of Mathematics" (PDF). Notices of the American Mathematical Society. 66 (8): 1. doi:10.1090/noti1928.
  7. ^ Berton, Justin (March 11, 2009). "Any way you slice it, pi's transcendental". San Francisco Chronicle. Retrieved March 18, 2011.
  8. ^ Borwein, Jonathan (March 10, 2011). "The infinite appeal of pi". Australian Broadcasting Corporation. Retrieved March 13, 2011.
  9. ^ Apollo, Adrian (March 10, 2007). "A place where learning pi is a piece of cake" (PDF). The Fresno Bee.
  10. ^ "Exploratorium 22nd Annual Pi Day". Exploratorium. Archived from the original on March 14, 2011. Retrieved January 31, 2011.
  11. ^ McCullagh, Declan (March 11, 2009). "National Pi Day? Congress makes it official". Politics and Law. CNET News. Retrieved March 14, 2009.
  12. ^ "Pi Day". Google Doodles. Retrieved October 9, 2012.
  13. ^ "30th Anniversary of Pi Day!". www.google.com. Retrieved March 19, 2018.
  14. ^ Purworini, D. (2016). Pi Day celebration by local scientists in Indonesia. Vol. 7. Anak Sudarti Foundation Bulletin. pp. 7–8.{{cite book}}: CS1 maint: location missing publisher (link)
  15. ^ Main, Douglas (March 14, 2014). "It's Not Just Pi Day, It's Pi Month!". Popular Science. Retrieved July 22, 2014.
  16. ^ "Pi Month Celebration & Circle of Discovery Award Presentation | College of Computer, Mathematical, and Natural Sciences". Cmns.umd.edu. March 11, 2014. Retrieved July 22, 2014.
  17. ^ Mack, Eric (March 14, 2015). "Celebrate The Only Super Pi Day Of The Century". Forbes. Retrieved March 14, 2019.
  18. ^ Ro, Sam (March 13, 2014). "March 14, 2015 Will Be A Once-In-A-Century Thrill For Math Geeks". Business Insider. Retrieved March 13, 2014.
  19. ^ Rosenthal, Jeffrey S. (February 2015). "Pi Instant". Math Horizons. 22 (3): 22. doi:10.4169/mathhorizons.22.3.22. S2CID 218542599.
  20. ^ Smith, K.N. "Wednesday's Google Doodle Celebrates Pi Day". Forbes.
  21. ^ "Celebrate Pi Day With These Deals Around North Texas". NBC DFW. March 13, 2021. Retrieved May 14, 2022.
  22. ^ "Honiton Community College Pi Day – Jazmin Year 9". YouTube. Archived from the original on October 17, 2013. Retrieved July 22, 2013.
  23. ^ "HCC Celebrate International Pi Day". Honitoncollege.devon.sch.uk. Archived from the original on February 22, 2014. Retrieved July 22, 2013.
  24. ^ McClan, Erin (March 14, 2007). "Pi fans meet March 14 (3.14, get it?)". NBC News. Retrieved January 24, 2008.
  25. ^ "I have SMASHING news!". MIT Admissions. March 7, 2012. Retrieved March 12, 2012.
  26. ^ McGann, Matt (March 13, 2012). "Pi Day, Tau Time". MIT Admissions. Retrieved March 18, 2012.
  27. ^ "Keep your eyes to the skies this Pi Day". MIT Admissions. March 6, 2015. Retrieved March 14, 2018.
  28. ^ "[Pinned] This is the way...to check your decisions". MIT Admissions. March 10, 2020. Retrieved March 14, 2020.
  29. ^ a b "Princeton Pi Day & Einstein Birthday Party". Princeton Regional Convention and Visitors Bureau. Retrieved February 9, 2019.
  30. ^ "Pi Approximation Day is celebrated today". Today in History. Verizon Foundation. Archived from the original on December 1, 2010. Retrieved January 30, 2011.
  31. ^ "Tau Day: Why you should eat twice the pie". Archived from the original on January 12, 2013.
  32. ^ "It's Pi Day today. But these people say we should refuse to celebrate it". The Independent. March 13, 2018. Archived from the original on May 26, 2022. Retrieved March 14, 2018.
  33. ^ "Pi Day Turns 25: Why We Celebrate an Irrational Number". March 14, 2013. Archived from the original on March 14, 2013. Retrieved March 14, 2018.
  34. ^ BMJ (June 22, 2018). "Jeffrey Aronson: When I use a word ... The Days of Pi". The BMJ. Retrieved May 2, 2023.
  35. ^ Bartholomew, Randyn Charles. Why Tau Trumps Pi.
  36. ^ Landau, Elizabeth. "In case Pi Day wasn't enough, it's now 'Tau Day' on the Internet". CNN.
  37. ^ "Tau Day – Come Eat Twice the (Pi)e".
  38. ^ "Pi Day – Fun Holiday". Timeanddate.com. Retrieved March 13, 2022.

External links[edit]