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Pi Day
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<h2 id="history">History</h2> <p>In 1988, the earliest known official or large-scale celebration of Pi Day was organized by <a href="/facts/Larry_Shaw_(Pi)/JjL3VmaS">Larry Shaw</a> at the <a href="/facts/Exploratorium/FGVLkbIc">San Francisco Exploratorium</a>,<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> where Shaw worked as a <a href="/facts/Physicist/cQcgvSIm">physicist</a>,<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> with staff and public marching around one of its circular spaces, then consuming fruit pies.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> The Exploratorium continues to hold Pi Day celebrations.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p><p>On March 12, 2009, the U.S. House of Representatives passed a <a href="/facts/Non-binding_resolution/CYcn8WGl">non-binding resolution</a> (111 H. Res. 224),<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> recognizing March 14, 2009, as National Pi Day.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> For Pi Day 2010, Google presented a <a href="/facts/Google_Doodle/3wysmHgU">Google Doodle</a> celebrating the holiday, with the word Google laid over images of circles and pi symbols;<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> and for the 30th anniversary in 2018, it was a <a href="/facts/Dominique_Ansel/PyroIV7D">Dominique Ansel</a> pie with the <a href="/facts/Circumference/r1rntU0f">circumference</a> divided by its <a href="/facts/Diameter/6uNn4VmU">diameter</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p><p>Some observed the entire month of March 2014 (3/14) as "Pi Month".<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a><a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> In the year 2015, March 14 was celebrated as "Super Pi Day".<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> 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,<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> and later that second, "Pi Instant" represented all of π's digits.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> </p> <h2 id="observance">Observance</h2> <p>Pi Day has been observed in many ways, including eating <a href="/facts/Pie/cVLNoM3p">pie</a>, <a href="/facts/Pieing/xwy1m0mz">throwing pies</a> and discussing the significance of the number π.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> The first two are due to a <a href="/facts/Pun/97K1L3yE">pun</a> based on the words "pi" and "pie" being <a href="/facts/Homophone/6zEo7t7c">homophones</a> in English ( /paɪ/), and the coincidental circular shape of many pies.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a><a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> Many <a href="/facts/Pizza/whX3st4e">pizza</a> and pie restaurants offer discounts, deals, and free products on Pi Day.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> Also, some schools hold competitions as to which student can <a href="/facts/Piphilology/H4lwryTR">recall pi to the highest number of decimal places</a>.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a><a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> </p><p>The <a href="/facts/Massachusetts_Institute_of_Technology/Xk49vNA8">Massachusetts Institute of Technology</a> has often mailed its <a href="/facts/College_admissions_in_the_United_States/rwXQqmkV">application decision letters</a> to prospective students for delivery on Pi Day.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> 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 π and 𝜏 equally.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a><a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> In 2015, the regular decisions were put online at 9:26 am, following that year's "pi minute",<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> and in 2020, regular decisions were released at 1:59 pm, making the first six digits of pi.<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a> </p><p><a href="/facts/Princeton%2c_New_Jersey/fceTzdde">Princeton, New Jersey</a>, hosts numerous events in a combined celebration of Pi Day and <a href="/facts/Albert_Einstein/CNTet8qu">Albert Einstein</a>'s birthday, which is also March 14.<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a> Einstein lived in Princeton for more than twenty years while working at the <a href="/facts/Institute_for_Advanced_Study/jQQCURKt">Institute for Advanced Study</a>. In addition to pie eating and recitation contests, there is an annual Einstein look-alike contest.<a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a> </p><p>In 2024, the <a href="/facts/Recreational_mathematics/p2b8zl2J">recreational mathematician</a> <a href="/facts/Matt_Parker/Sj4pTjWw">Matt Parker</a> and a team of hundreds of volunteers at <a href="/facts/City_of_London_School/vBWKsN02">City of London School</a> spent six days calculating 139 correct digits of pi by hand, in what Parker claimed was "the biggest hand calculation in a century".<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a><a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> On 15 August 2024, the <a href="/facts/Main-belt_asteroid/YHAq2Eh3">main-belt asteroid</a> <a href="/facts/List_of_minor_planets%3a_314001%25E2%2580%2593315000/2C3lBF9W">314159 Mattparker</a><a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> was named in his honor. The citation highlights Parker's biennial "Pi Day challenges", stating that they have helped to popularize mathematics.<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a><a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a> </p> <h2 id="alternative-dates">Alternative dates</h2> <p>Pi Day is frequently observed on March 14 (3/14 in the <i>month/day</i> date format), but related celebrations have been held on alternative dates. </p><p>Pi Approximation Day is observed on July 22 (22/7 in the <i>day/month</i> date format), since the <a href="/facts/Fraction_(mathematics)/ghnQE9B3">fraction</a> 22⁄7 is a common <a href="/facts/Approximations_of_%25CF%2580/03SQhgcM">approximation of π</a>, which is accurate to two decimal places and dates from <a href="/facts/Archimedes/sIeMhSVF">Archimedes</a>.<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a> In Indonesia, <a href="/facts/Date_and_time_representation_by_country/p3VnlGUG">a country that uses the DD/MM/YYYY date format</a>, some people celebrate Pi Day every July 22.<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a> </p><p><a href="/facts/Tau_(mathematical_constant)/QczxAyuM">Tau</a> Day, also known as Two-Pi Day,<a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a> is observed on June 28 (6/28 in the <i>month/day</i> format).<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a> The number <a href="/facts/Turn_(angle)/QczxAyuM">𝜏</a>, denoted by the Greek letter <a href="/facts/Tau/gfvnmJoH">tau</a>, is the ratio of a circle's <a href="/facts/Circumference/r1rntU0f">circumference</a> to its <a href="/facts/Radius/9Gr9deYD">radius</a>; it equals 2π, a common multiple in mathematical formulae, and approximately equals 6.28. Some have argued that 𝜏 is the clearer and more fundamental constant and that Tau Day should be celebrated alongside or instead of Pi Day.<a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a><a class="footnote-ref" id="fnref:42" href="#fn:42"><sup>42</sup></a><a class="footnote-ref" id="fnref:43" href="#fn:43"><sup>43</sup></a> Celebrants of this date jokingly suggest eating "twice the pie".<a class="footnote-ref" id="fnref:44" href="#fn:44"><sup>44</sup></a><a class="footnote-ref" id="fnref:45" href="#fn:45"><sup>45</sup></a><a class="footnote-ref" id="fnref:46" href="#fn:46"><sup>46</sup></a> </p><p>Some also celebrate π on November 10, since it is the 314th day of the year (in leap years, on November 9).<a class="footnote-ref" id="fnref:47" href="#fn:47"><sup>47</sup></a> </p> <h2 id="gallery">Gallery</h2> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Lists_of_holidays/QMlYetUI">Lists of holidays</a></li> <li><a href="/facts/National_Mathematics_Day_(India)/X05obdeM">National Mathematics Day (India)</a> – Celebration that commemorates the birthday of Srinivasa Ramanujan</li> <li><a href="/facts/Mole_Day/R7nuGoL6">Mole Day</a> – Unofficial holiday related to chemistry</li> <li><a href="/facts/Sequential_time/cllARMuG">Sequential time</a></li> <li><a href="/facts/Square_Root_Day/g7wgGQMN">Square Root Day</a></li> <li><a href="/facts/Doomsday_rule/5TXr6fsc">Doomsday rule</a> – Way of calculating the day of the week of a given date</li> <li><a href="/facts/Programmers%2527_Day/o75gPqbY">Programmers' Day</a></li></ul> <h2 id="notes">Notes</h2> <h2 id="external-links">External links</h2> Wikimedia Commons has media related to Pi Day. Look up <i>Pi Day</i> in Wiktionary, the free dictionary. <ul><li><a href="http://www.exploratorium.edu/pi/">Exploratorium's Pi Day Web Site</a></li> <li><a href="https://www.idm314.org">Official website of the International Day of Mathematics</a></li> <li><a href="https://en.unesco.org/commemorations/mathematics">UNESCO page on the International Day of Mathematics</a></li> <li><a href="https://www.npr.org/sections/thetwo-way/2010/03/pi_day.html/">NPR provides a "Pi Rap" audiovideo</a></li> <li><a href="http://www.idm314.org/">Pi Day</a></li> <li><a href="http://www.math.utep.edu/Faculty/lesser/piday.html">Professor Lesser's Pi Day page</a></li> <li><a href="https://www.eeo.cn/webcast.php?courseKey=8a44be5970c129ba">数学漫谈</a> (A Tour of Mathematics), a public lecture (in Chinese) delivered by Professor <a href="http://lsec.cc.ac.cn/~yyx/">Ya-xiang Yuan</a> (President of <a href="/facts/International_Council_for_Industrial_and_Applied_Mathematics/IDdHIb08">International Council for Industrial and Applied Mathematics</a>) on 14 March 2020, the first International Day of Mathematics (<a href="https://web.archive.org/web/20210706210819/ftp://lsec.cc.ac.cn/pub/home/yyx/2020.03.14.15.pdf">slides</a>)</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Bellos, Alex (March 14, 2015). "Pi Day 2015: a sweet treat for maths fans". The Guardian. Retrieved March 14, 2016. <a href="https://www.theguardian.com/science/2015/mar/13/pi-day-celebration-maths-fans-language-memory-contests" target="_blank">https://www.theguardian.com/science/2015/mar/13/pi-day-celebration-maths-fans-language-memory-contests</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Nedräkning mot internationella Pi-dagen". Swedish national radio company (in Swedish). March 14, 2015. <a href="http://sverigesradio.se/sida/avsnitt/514543?programid=412" target="_blank">http://sverigesradio.se/sida/avsnitt/514543?programid=412</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>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 <a href="http://thomas.loc.gov/cgi-bin/query/z?c111:H.RES.224:" target="_blank">http://thomas.loc.gov/cgi-bin/query/z?c111:H.RES.224:</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"International Day of Mathematics". UNESCO. March 4, 2020. <a href="https://en.unesco.org/commemorations/mathematics" target="_blank">https://en.unesco.org/commemorations/mathematics</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Rousseau, Christiane (September 1, 2019). "International Day of Mathematics" (PDF). Notices of the American Mathematical Society. 66 (8): 1. doi:10.1090/noti1928. <a href="https://www.ams.org/journals/notices/201908/rnoti-p1306.pdf" target="_blank">https://www.ams.org/journals/notices/201908/rnoti-p1306.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Berton, Justin (March 11, 2009). "Any way you slice it, pi's transcendental". San Francisco Chronicle. Retrieved March 18, 2011. <a href="https://www.sfgate.com/science/article/Any-way-you-slice-it-pi-s-transcendental-3169091.php" target="_blank">https://www.sfgate.com/science/article/Any-way-you-slice-it-pi-s-transcendental-3169091.php</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Borwein, Jonathan (March 10, 2011). "The infinite appeal of pi". Australian Broadcasting Corporation. Retrieved March 13, 2011. <a href="/wiki/Jonathan_Borwein" target="_blank">/wiki/Jonathan_Borwein</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Apollo, Adrian (March 10, 2007). "A place where learning pi is a piece of cake" (PDF). The Fresno Bee. <a href="http://apollotutoring.com/pi_day.pdf" target="_blank">http://apollotutoring.com/pi_day.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Exploratorium 22nd Annual Pi Day". Exploratorium. Archived from the original on March 14, 2011. Retrieved January 31, 2011. <a href="https://web.archive.org/web/20110314012746/http://www.exploratorium.edu/pi/index.html" target="_blank">https://web.archive.org/web/20110314012746/http://www.exploratorium.edu/pi/index.html</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>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 <a href="http://thomas.loc.gov/cgi-bin/query/z?c111:H.RES.224:" target="_blank">http://thomas.loc.gov/cgi-bin/query/z?c111:H.RES.224:</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>McCullagh, Declan (March 11, 2009). "National Pi Day? Congress makes it official". Politics and Law. CNET News. Retrieved March 14, 2009. <a href="http://news.cnet.com/8301-13578_3-10194354-38.html?part=rss&subj=news&tag=2547-1_3-0-5" target="_blank">http://news.cnet.com/8301-13578_3-10194354-38.html?part=rss&subj=news&tag=2547-1_3-0-5</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"Pi Day". Google Doodles. Retrieved October 9, 2012. <a href="https://doodles.google/doodle/pi-day/" target="_blank">https://doodles.google/doodle/pi-day/</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"30th Anniversary of Pi Day!". www.google.com. Retrieved March 19, 2018. <a href="https://doodles.google/doodle/30th-anniversary-of-pi-day/" target="_blank">https://doodles.google/doodle/30th-anniversary-of-pi-day/</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Main, Douglas (March 14, 2014). "It's Not Just Pi Day, It's Pi Month!". Popular Science. Retrieved July 22, 2014. <a href="http://www.popsci.com/article/science/its-not-just-pi-day-its-pi-month" target="_blank">http://www.popsci.com/article/science/its-not-just-pi-day-its-pi-month</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Jencasa (March 11, 2014). "Pi Month Celebration & Circle of Discovery Award Presentation | College of Computer, Mathematical, and Natural Sciences". College of Computer, Mathematical, and Natural Sciences. Cmns.umd.edu. Retrieved July 22, 2014. <a href="http://cmns.umd.edu/news-events/events/1774" target="_blank">http://cmns.umd.edu/news-events/events/1774</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Mack, Eric (March 14, 2015). "Celebrate The Only Super Pi Day Of The Century". Forbes. Retrieved March 14, 2019. <a href="https://www.forbes.com/sites/ericmack/2015/03/14/happy-super-pi-day-heres-how-to-celebrate/" target="_blank">https://www.forbes.com/sites/ericmack/2015/03/14/happy-super-pi-day-heres-how-to-celebrate/</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>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. <a href="http://www.businessinsider.com/pi-day-2015-2014-3" target="_blank">http://www.businessinsider.com/pi-day-2015-2014-3</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Rosenthal, Jeffrey S. (February 2015). "Pi Instant". Math Horizons. 22 (3): 22. doi:10.4169/mathhorizons.22.3.22. S2CID 218542599. <a href="http://probability.ca/jeff/writing/PiInstant.html" target="_blank">http://probability.ca/jeff/writing/PiInstant.html</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Anderson, Curt (March 14, 2024). "What's Pi Day all about? Math, science, pies and more". Associated Press. Archived from the original on March 14, 2024. Retrieved March 14, 2025. <a href="https://apnews.com/article/pi-day-celebration-math-infinite-number-f426c8659529cb07655b5f07b99ce1dd" target="_blank">https://apnews.com/article/pi-day-celebration-math-infinite-number-f426c8659529cb07655b5f07b99ce1dd</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Landau, Elizabeth (March 12, 2010). "On Pi Day, one number 'reeks of mystery'". CNN. Retrieved March 14, 2018. <a href="/wiki/Elizabeth_Landau" target="_blank">/wiki/Elizabeth_Landau</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Smith, K.N. "Wednesday's Google Doodle Celebrates Pi Day". Forbes. <a href="https://www.forbes.com/sites/kionasmith/2018/03/14/wednesdays-google-doodle-celebrates-pi-day/" target="_blank">https://www.forbes.com/sites/kionasmith/2018/03/14/wednesdays-google-doodle-celebrates-pi-day/</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>"Celebrate Pi Day With These Deals Around North Texas". NBC DFW. March 13, 2021. Retrieved May 14, 2022. <a href="https://www.nbcdfw.com/news/local/celebrate-pi-day-with-these-deals-around-north-texas/2578077/" target="_blank">https://www.nbcdfw.com/news/local/celebrate-pi-day-with-these-deals-around-north-texas/2578077/</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>"Honiton Community College Pi Day – Jazmin Year 9". YouTube. Archived from the original on October 17, 2013. Retrieved July 22, 2013. <a href="https://web.archive.org/web/20131017125801/http://www.youtube.com/watch?v=dfM1i9_Un_Y" target="_blank">https://web.archive.org/web/20131017125801/http://www.youtube.com/watch?v=dfM1i9_Un_Y</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>"HCC Celebrate International Pi Day". Honitoncollege.devon.sch.uk. Archived from the original on February 22, 2014. Retrieved July 22, 2013. <a href="https://web.archive.org/web/20140222033538/http://www.honitoncollege.devon.sch.uk/index.php/about-honiton-community-college/10-honiton-community-college-news/146-hcc-international-pi-day-champions" target="_blank">https://web.archive.org/web/20140222033538/http://www.honitoncollege.devon.sch.uk/index.php/about-honiton-community-college/10-honiton-community-college-news/146-hcc-international-pi-day-champions</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>McClan, Erin (March 14, 2007). "Pi fans meet March 14 (3.14, get it?)". NBC News. Archived from the original on September 27, 2013. Retrieved January 24, 2008. <a href="https://web.archive.org/web/20130927144029/http://www.nbcnews.com/id/17605924/" target="_blank">https://web.archive.org/web/20130927144029/http://www.nbcnews.com/id/17605924/</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></p></li> <li id="fn:26"><p>"I have SMASHING news!". MIT Admissions. March 7, 2012. Retrieved March 12, 2012. <a href="http://mitadmissions.org/blogs/entry/i-have-smashing-news" target="_blank">http://mitadmissions.org/blogs/entry/i-have-smashing-news</a> <a href="#fnref:26" class="footnote-back-ref">↩</a></p></li> <li id="fn:27"><p>McGann, Matt (March 13, 2012). "Pi Day, Tau Time". MIT Admissions. Retrieved March 18, 2012. <a href="http://mitadmissions.org/blogs/entry/pi-day-tau-time" target="_blank">http://mitadmissions.org/blogs/entry/pi-day-tau-time</a> <a href="#fnref:27" class="footnote-back-ref">↩</a></p></li> <li id="fn:28"><p>"Keep your eyes to the skies this Pi Day". MIT Admissions. March 6, 2015. Retrieved March 14, 2018. <a href="http://mitadmissions.org/blogs/entry/keep-your-eyes-to-the-skies" target="_blank">http://mitadmissions.org/blogs/entry/keep-your-eyes-to-the-skies</a> <a href="#fnref:28" class="footnote-back-ref">↩</a></p></li> <li id="fn:29"><p>"[Pinned] This is the way...to check your decisions". MIT Admissions. March 10, 2020. 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