--- title: Today Is Pi Day 2018. Here's What You Need to Know description: March 14 is Pi Day 2018 — pi, not pie — and Google is marking the 30th anniversary of the math-inspired holiday with a special Doodle canonical: https://time.com/5198663/30th-anniversary-of-pi-day-2018-facts/ author: Eli Meixler article:opinion: false article:content_tier: free article:published_time: 2018-03-14T03:39:45.000Z article:modified_time: 2023-12-12T21:15:35.000Z og:title: Today Is Pi Day 2018. Here's What You Need to Know og:description: Peter Trueb calculated pi to 22.4 trillion digits og:url: https://time.com/5198663/30th-anniversary-of-pi-day-2018-facts/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt81c5862a9c1c562f/69892ab897cdff19906b4a71/google-doodle-pi-day.jpg?branch=production&width=818&quality=75&auto=webp&crop=16:9 og:image:width: 818 og:image:height: 460 og:image:alt: google-doodle-pi-day og:type: article twitter:card: summary_large_image twitter:title: Today Is Pi Day 2018. Here's What You Need to Know twitter:description: Peter Trueb calculated pi to 22.4 trillion digits twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt81c5862a9c1c562f/69892ab897cdff19906b4a71/google-doodle-pi-day.jpg?branch=production&width=818&quality=75&auto=webp&crop=16:9 ---  # Today Is the 30th Anniversary of Pi Day. Here's What You Should Know About the Irrational Number > Sponsored content. 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It curates the day's top headlines with TIME's reporting and analysis across politics, world affairs, business, health and culture. It is free to join at time.com/newsletters. #### How do I sign up for The Brief? The Brief is available free at time.com/newsletters, where readers can select it along with any of TIME's other six newsletters. There is no subscription required to receive it. #### Is The Brief free? Yes. The Brief is a free daily email newsletter from TIME. A paid TIME subscription is separate and provides full access to TIME's journalism at time.com/subscribe-agent. #### Who writes The Brief? The Brief is led by editor Richard Hall and draws on reporting from TIME's newsroom. Every edition is assembled by TIME editors rather than generated automatically. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-brief-2026q3/newsletters?i=51bf2df3-2888-476e-9ffc-afdf559103dd&cr=time-nl-brief-2026q3-v1) by [Eli Meixler](https://time.com/author/eli/) ## Eli Meixler Updated: Dec 12, 2023 9:15 PM UTCPublished: Mar 14, 2018 3:39 AM UTC  Google by [Eli Meixler](https://time.com/author/eli/) ## Eli Meixler Updated: Dec 12, 2023 9:15 PM UTCPublished: Mar 14, 2018 3:39 AM UTC March 14, 2018, is [Pi Day](http://www.piday.org/) — that’s pi, not pie — and on Wednesday, Google marks the 30th anniversary of the math-inspired holiday with a [special Doodle](https://www.google.com/doodles/30th-anniversary-of-pi-day). Pi, denoted by the Greek letter “π”, has been part of human knowledge for millennia, but it wasn’t until 1988 that physicist Larry Shaw organized what is now recognized as the first “Pi Day” celebration at the San Francisco Exploratorium science museum. Shaw chose March 14, or 3.14 — the first three digits of pi — as Pi Day. Shaw [died last year](https://www.sfgate.com/bayarea/article/Memorial-service-set-for-Pi-Day-creator-Larry-Shaw-12206726.php), but Pi Day is still [celebrated ](http://time.com/4699479/pi-day-2017-history-origins/)by lovers of mathematics around the world. As we celebrate again in 2018, here are some Pi Day facts you should know. ## What Is Pi? Pi represents the ratio of a circle’s circumference to its diameter. It’s an important part of the foundation of mathematics, most importantly geometry, where pi is key to equations calculating the area of a circle, A = πr2, and the volume of a cylinder, V = πr2h. > [](https://twitter.com/maximaxoo/status/973697772904906752) ## The History of Pi Various [ancient civilizations](https://gizmodo.com/a-brief-history-of-pi-1610160819) calculated approximations of pi, including the Egyptians, Babylonians, and there’s even a reference to the dimensions of a circle in the [Bible](https://www.biblegateway.com/passage/?search=1+Kings+7%3A23&version=KJV), but the first calculation of pi as 3.14 is attributed to [Greek mathematician Archimedes](http://content.time.com/time/magazine/article/0,9171,908175,00.html), who lived in the third century B.C.. It was also independently determined by Chinese mathematician Zu Chongzhi (429–501), who [computed pi ](https://web.archive.org/web/20070929095635/http://203.72.198.245/web/Content.asp?ID=43669&Query=1)to six decimal places. Mathematicians adopted the symbol π for the expression in the 18th century: Welsh mathematics teacher William Jones is [often credited](https://www.historytoday.com/patricia-rothman/william-jones-and-his-circle-man-who-invented-pi) with the first use of the symbol in 1706. ## How Many Numbers Are in Pi? Pi is a mathematical constant, meaning it isn’t changed by the size of the numbers it’s used to equate, and it is irrational, meaning it has an infinite number of digits that never repeat. The rise of computing technology has led to an arms race of sorts to calculate ever more digits of pi: the current record was set last year by Christian physicist Peter Trueb, [calculated](https://arxiv.org/abs/1612.00489) pi to 22.4 trillion digits — 22,459,157,718,361, to be exact — outpacing the previous record set in 2013 by 9 million digits. But adding new digits is little more than a pastime for mathematics fanatics: NASA’s Jet Propulsion lab [only uses 15 digits](https://www.jpl.nasa.gov/edu/news/2016/3/16/how-many-decimals-of-pi-do-we-really-need/) to calculate interplanetary travel, while mathematician James Grime argues that [just 39 digits of pi](https://www.youtube.com/watch?v=FpyrF%5FCi2TQ) is enough to calculate the circumference of the known universe. ## How Is Pie Day Celebrated? Pi Day was [officially recognized](https://www.congress.gov/bill/111th-congress/house-resolution/224/text) by Congress in 2009, and it’s inspired quirky and pun-filled celebrations, including eating circular treats, from fruit pies to pizza, as well as dressing like [Albert Einstein](http://time.com/4228178/albert-einstein-birthday/), whose birthday serendipitously falls on the math-imbued day. San Francisco’s Exploratorium also hosts an annual day of [pi-inspired activities](https://www.exploratorium.edu/pi). The Massachusetts Institute of Technology releases its [undergraduate admissions ](http://mitadmissions.org/blogs/entry/pi-day-tau-time)decisions on Pi Day, and starting in 2012, it began sending the verdicts at 6:28 pm, or “Tau time,” for the mathematical equation 2π. This year, NASA is inviting math whizzes to compete in its “Pi in the Sky” [challenge](https://www.jpl.nasa.gov/edu/nasapidaychallenge/) to solve a series of interplanetary math problems. > [](https://twitter.com/RosannaPansino/status/973625345336254464) > [](https://twitter.com/dflory71/status/973715673397583874) Wednesday’s Doodle is based on a pi-inspired dish, salted caramel apple pie, courtesy of [Cronut](http://time.com/3475343/now-you-can-make-cronuts-at-home-with-this-official-recipe/) creator and [pastry pioneer ](http://time.com/3837992/dominique-ansel-kitchen-cronut/)Dominique Ansel. ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/5198663/30th-anniversary-of-pi-day-2018-facts/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/5198663/30th-anniversary-of-pi-day-2018-facts/"},"headline":"Today Is the 30th Anniversary of Pi Day. 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