ObservanceSunday, March 14, 2027
Pi Day
- Date
- Recurs
- Every year on March 14
- Category
- Celebration
Pi Day falls on March 14, because 3/14 matches the first three digits of pi, the ratio of a circle's circumference to its diameter. It began in 1988 as an in-house celebration at the Exploratorium, San Francisco's hands-on science museum, and spread from there into classrooms worldwide. It is one of the few modern holidays whose origin is fully documented, down to the man who thought of it and the pies on the table.
History
In 1988, three years after the death of Exploratorium founder Frank Oppenheimer, museum staff gathered at a retreat in Monterey, California, to regroup. There Larry Shaw connected March 14 with the digits of pi. The Exploratorium describes him as a former staff physicist, tinkerer, and media specialist; the San Francisco Chronicle called him the museum's technical curator of 33 years. On the first Pi Day, at 1:59 — the digits that follow 3.14 — Shaw and his wife, Catherine, set out a table of fruit pies and a tea urn on the museum floor.
The rituals accumulated afterward. Shaw built the Pi Shrine, a circular brass plaque set in a circular classroom made of circular cinderblocks, and led a parade through the museum with a boombox playing the digits of pi to "Pomp and Circumstance," ending by circling the shrine 3.14 times. A few years in, Shaw's daughter Sara noticed that March 14 is also Albert Einstein's birthday, and a chorus of "Happy Birthday" to Einstein joined the program. Shaw led the parade every year until his death in 2017, known around the museum as the Prince of Pi.
Washington arrived twenty-one years late and did less than it is credited with. Representative Bart Gordon of Tennessee introduced House Resolution 224 on March 9, 2009; the House agreed to it three days later, 391 to 10, on a motion to suspend the rules. The resolution supports "the designation of a 'Pi Day' and its celebration around the world," recognizes the National Science Foundation's math and science programs, and encourages schools to teach the day. It creates no holiday, it never went to the Senate, and it mentions neither the Exploratorium nor Einstein. Both the Exploratorium and NASA describe it more loosely than its own text supports — as Pi Day becoming "an official U.S. national holiday," or Congress "officially designating" the date.
Timeline
- 1988 — At a staff retreat in Monterey, Larry Shaw links March 14 with 3.14. He and Catherine Shaw mark the first Pi Day at 1:59 with fruit pies and a tea urn.
- 2009 — H. Res. 224 is introduced on March 9 and agreed to by the House on March 12, 391 to 10, supporting the designation of a Pi Day.
- 2014 — NASA's Jet Propulsion Laboratory runs the first NASA Pi Day Challenge.
- 2017 — Larry Shaw dies, having led the parade every year since the first.
- 2019 — UNESCO proclaims March 14 the International Day of Mathematics on November 26, at the 40th session of its General Conference.
- 2020 — The first International Day of Mathematics is held, on March 14.
How to observe
Try the NASA Pi Day Challenge. NASA's Jet Propulsion Laboratory has run one every March since 2014: illustrated problems that use pi on real mission data, pitched at grades four through twelve, with answers posted the next day.
Settle the argument about how many digits anyone needs. JPL's then-chief engineer for mission operations, Marc Rayman, answered it in public: for interplanetary navigation, the laboratory's most demanding work, they use 3.141592653589793 — fifteen decimal places. At that precision a circle 125 billion miles around comes out wrong by a little over half an inch, and thirty-seven places would size the known universe to within a hydrogen atom.
If you are near San Francisco, the Exploratorium still holds its Pi Procession at 1:59 p.m., circling the Pi Shrine 3.14 times, with a free slice of pie after.
And note what else the date carries: since 2020 March 14 has also been the International Day of Mathematics, which publishes a yearly theme and classroom activities at idm314.org.
Frequently asked questions
Is Pi Day an official federal holiday?
No. The House of Representatives passed a resolution in 2009 supporting the designation of a Pi Day, but a House resolution is not law. It never went to the Senate, it created no holiday, and federal offices, banks, and schools operate normally on March 14.
Who started Pi Day?
Larry Shaw, at the Exploratorium in San Francisco, in 1988. He came up with the idea at a staff retreat in Monterey and marked the first one with his wife, Catherine, at a table of fruit pies set out at 1:59.
Why March 14?
Written American-style, the date is 3/14, the first three digits of pi. The International Mathematical Union notes the limit of that logic: in countries that write the day first, the date is 14/3 and the joke does not land.
How many digits of pi does NASA use?
For its highest-accuracy calculations, interplanetary navigation, JPL uses 3.141592653589793 — fifteen decimal places. Rounding there would misjudge a circle 125 billion miles in circumference by about half an inch.
Is Pi Day the same thing as the International Day of Mathematics?
They share the date but not the history. UNESCO proclaimed March 14 the International Day of Mathematics in November 2019, choosing the date precisely because it was already being celebrated as Pi Day; the first observance was in 2020.
When is Pi Day?
| Year | Date | Day |
|---|---|---|
| 2027 | March 14 | Sunday |
| 2028 | March 14 | Tuesday |
| 2029 | March 14 | Wednesday |
| 2030 | March 14 | Thursday |
| 2031 | March 14 | Friday |
Sources
- Exploratorium, A Slice of Pi (Pi) Day History — https://www.exploratorium.edu/pi-day/pi-day-history → the 1988 Monterey retreat and Frank Oppenheimer's death three years earlier; Larry Shaw described as former staff physicist, tinkerer and media specialist; the first Pi Day at 1:59 with Catherine Shaw, fruit pies and a tea urn; the Pi Shrine; the boombox parade to "Pomp and Circumstance" and circling the shrine 3.14 times; daughter Sara and the Einstein birthday; Shaw's death in 2017; "Prince of Pi"; the claim that Pi Day became "an official U.S. national holiday" in 2009.
- Exploratorium, Pi (Pi) Day — https://www.exploratorium.edu/pi → "Founded in 1988 at the Exploratorium"; the present-day Pi Procession at 1:59 p.m., circling the Pi Shrine 3.14 times, "Happy Birthday" to Einstein, and a free slice of pie.
- San Francisco Chronicle (SFGate), Pi Day's history is rooted in the Bay Area, thanks to Exploratorium curator Larry Shaw — https://www.sfgate.com/bayarea/article/Pi-Day-s-history-is-rooted-in-the-Bay-Area-13688884.php → Shaw as "technical curator at the Exploratorium for 33 years"; the 1988 retreat; the inaugural table of fruit pies and tea urn; the "Prince of Pi" nickname; Shaw's death in 2017; Congressional recognition in 2009.
- U.S. Government Publishing Office, H. Res. 224, 111th Congress, Supporting the designation of Pi Day, and for other purposes (introduced in House) — https://www.govinfo.gov/content/pkg/BILLS-111hres224ih/html/BILLS-111hres224ih.htm → sponsor Mr. Gordon of Tennessee; introduced March 9, 2009; the full resolving clauses; no mention of the Exploratorium or Einstein anywhere in the text.
- Office of the Clerk, U.S. House of Representatives, Final Vote Results for Roll Call 124 — https://clerk.house.gov/evs/2009/roll124 → H. Res. 224 agreed to March 12, 2009 on a motion to suspend the rules; 391 yea, 10 nay, 30 not voting.
- NASA Jet Propulsion Laboratory, 10 Years of NASA's Pi Day Challenge — https://www.jpl.nasa.gov/edu/resources/teachable-moment/10-years-of-nasas-pi-day-challenge/ → 2023 as the tenth installment, placing the first in 2014; the challenge's grade range and format; NASA's description of the 2009 resolution as "officially designating March 14 as Pi Day."
- NASA Jet Propulsion Laboratory, How Many Decimals of Pi Do We Really Need? (Marc Rayman) — https://www.jpl.nasa.gov/edu/news/how-many-decimals-of-pi-do-we-really-need/ → 3.141592653589793 for JPL's highest-accuracy interplanetary navigation; the half-inch error on a circle roughly 125 billion miles around; 37 decimal places sufficient to size the known universe to a hydrogen atom; Rayman's title.
- International Mathematical Union, About the International Day of Mathematics — https://www.idm314.org/about → UNESCO's proclamation at the 40th session of the General Conference, November 26, 2019; first celebration March 14, 2020; March 14 chosen because it was already Pi Day; the day-first date-format caveat.
Rejected as sources: nationaltoday, nationaldaycalendar, checkiday, timeanddate, and content-farm or AI-generated listicles. The SFGate piece also states Shaw led the parade "for 38 years," which cannot be squared with a 1988 start and a 2017 death; that figure is not used here.
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