Pi Day Activities and History, Plus 13 Facts About the World's Most Interesting Number

Pi Day is celebrated every year on March 14—when the date can be written as 3.14 in U.S. date format notation. While some official events and celebrations will be curtailed by the novel coronavirus COVID-19, there's still plenty of reason to scarf some pie and celebrate the famous mathematical constant.

Pi, or the Greek letter π in mathematical notation, is a number describing the ratio between a circle's diameter and its circumference. All it takes to calculate pi is a simple formula—π = C/d, or pi equals a circle's circumference, divided by its diameter. The result is a number that can't be expressed with a simple fraction and stretches on infinitely beyond its decimal point. Here's pi, written out to its first 100 digits:

3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679

Pi Day Activities

The earliest official celebration of Pi Day was organized by physicist Larry Shaw and held in 1988 at the San Francisco Exploratorium. Attendees marched in circles and ate pies. The celebration is still held annually, but the 2020 Pi Day has been cancelled due to the spread of COVID-19. Despite that, there are still plenty of ways to celebrate Pi Day, either solo in quarantine or with your classroom.

Pizza parties and pie parties are a natural fit for celebrating Pi Day. A pie-baking contest, potluck or pie prizes are all great ways to promote math while eating tasty desserts.

Many classrooms also use the holiday as an opportunity to build a visual model of the ratio, by using a different colored piece of construction paper for each of the ten numerals, then linking them in a paper chain—the colors illustrate the randomization and patterns found throughout the sequence.

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British writer Daniel Tammet appearing at a 2013 Pi Day celebration in France. He holds the European record for reciting pi, to 22,514 digits. LIONEL BONAVENTURE/AFP via Getty Images

Pi Day is also a great opportunity to practice memorization: See who can memorize pi to the most digits, or practice some of the mnemonic techniques used by "piphilologists." Particularly popular are so-called "piems"—a portmanteau of "pi" and "poem." A piem is a poem in which the length of each word in sequence represents a digit of pi.

Here's a simple piem: "Now I need a drink, alcoholic of course, after the heavy lectures involving quantum mechanics."

Musician Andrew Huang even wrote a piem song, which reflects the first 101 digits of pi. Here's a version that's easy to use as a singalong:

There's also an entire micro-genre of short stories and longer prose works that operate on the same principle—a style called "Pilish." Pilish short stories include writer Mike Keith's poetic short story, "Cadaeic Cadenza," written in 1996. You can read it here.

TeachPi.org has more than 50 additional ideas for classrooms and educational opportunities related to Pi Day.

History of π (Pi)

While not every society celebrates Pi Day, every civilization in recorded history that has a mathematics of circles discovered and used an approximation of pi. Pi is even alluded to in the Bible, though only approximately. King Solomon's construction of the Temple in Jerusalem is described in I Kings, including a detailed description of the "Molten Sea"—a massive cast metal basin (enough for "two thousand baths") built atop statues of 12 bulls. It is described as having a 10-cubit diameter and a 30-cubit circumference, resulting in a calculation of pi equal to three. The Babylonians and Egyptians both had more accurate approximations of pi's value, but it was the ancient Greeks who showed the most interest in the ratio conceptually, as a fundamental building block of mathematics.

Described in The Penguin Dictionary of Curious and Interesting Numbers by David Wells as "the most famous and most remarkable of all numbers," pi is so much more than a description of the relation between a circle's circumference and diameter—it also possesses a number of other strange and interesting qualities that has made it central to mathematics throughout history and all over the world.

13 Interesting Facts about π (Pi)

  1. Archimedes calculated the value of pi to between 3.14085 and 3.14285 in the third century B.C., settling on 22/7 as a sufficient approximation.
  2. In the fifth century A.D., a more accurate value for pi was calculated by Chinese mathematician and astronomer Zu Chongzhi.
  3. The next breakthrough came in 1424, when Persian astronomer and mathematician Jamshid Kashani calculated pi to 17 digits.
  4. Around 1600, pi was extended to 35 digits by German-Dutch mathematician Ludolph van Ceulen. He was so proud of his "Ludolphine number" that it was inscribed on his tombstone.
  5. Using the Ludolphine number, it became theoretically possible to create a perfect circle, down to the atomic level.
  6. While previous calculations approximated pi by measuring the area of many-sided polygons—a geometric method invented by Archimedes—an algebraic formula for pi was discovered in 1592, with further refinements following over the subsequent century.
  7. Swiss mathematician and physicist Leonhard Euler, born 1707, formalized the use of the Greek letter π for pi—based on the Greek word for circumference, perimetros—following the symbol's usage by Welsh mathematician, and friend of Isaac Newton, William Jones.
  8. Mathematicians in the 18th and 19th centuries competed to calculate as many digits of pi as possible, as quickly as possible. Johann Dase, born 1824, calculated the constant to 200 digits in two months.
  9. The first electronic, digital "general purpose" computer ENIAC (Electronic Numerical Integrator and Computer) calculated pi to 2,037 places in 1949. It took 70 hours.
  10. The current world record is held by cybersecurity analyst Timothy Mullican, who used 303 days of computation to calculate pi to 50 trillion digits.
  11. Pi is an "irrational" number, meaning it cannot be expressed as a fraction of integers. It is infinite.
  12. A famous coincidental sequence of six 9's occurs in pi, starting at the 762nd digit past the decimal point.
  13. According to the Guinness World Records, Rajveer Meena of India holds the record for memorizing the most digits of π: 70,000. His 2015 recitation took 9 hours and 27 minutes.

Happy Pi Day everyone!