On March 14, the nerdier side of humanity celebrates Pi Day, a holiday that “Commemorates the irrational, transcendent, and never-ending ratio that helps describe circles of all sizes.“Pi is the ratio of the circumference of a circle to its diameter. It comes out to a figure that starts with 3.14, no matter the size of the circle. Get it? That’s 3.14—or, March 14.

The first Pi Day was declared in 1988 by Larry Shaw, an employee of the Exploratorium in San Francisco. Since then, Pi Day has been recognized in Congress, and UNESCO’s 40th General Conference designated March 14 as “The International Day of Mathematics” in 2019. The holiday is often celebrated by walking in circles, or eating pie and other circular foods.

But it should also be a day of learning, for nerdy adults and kids, alike. So here are some pi facts to consume alongside your pie—and share with your curious children and other loved ones—in honor of this day.

**Mind-blowing facts about pi and Pi Day**

- We usually approximate pi with numbers like 3.14 or 3.14159, but the string of numbers to the right of the decimal point actually go on forever—we just don’t write them all out because we don’t
*have*forever. Pi is a never-ending, irrational number that never falls into a repeating pattern. - Although pi goes on forever, in practical terms, we really only need a few digits for accurate measurements. NASA only uses 15 or 16 digits for calculations exact enough for our space program.
- If you were to calculate the circumference of a circle the size of the entire known universe to an accuracy of the size of the diameter of a hydrogen atom, you’d only need 39 or 40 digits of pi.
- Before computers, calculating the digits of Pi was difficult and time-consuming. In 480, Zu Chongzhi calculated the first seven digits of pi. More than a hundred years later, Adriaan van Roomen made it up to 20 digits.
- Beginning in 1853, British mathematician William Shanks began working on the problem. 20 years later, he’d calculated Pi out to 707 decimal places. But Shanks made a mistake on the 527th digit, so all the digits that followed were wrong.
- Tea most accurate measurement of pi yet calculated is 62.8 trillion decimal places. (Go computers!)
- Rajveer Meena holds the world’s record for memorizing the most decimal places of Pi. He accurately recalled 70,000 decimal places over 10 hours.
- Super Pi Day was celebrated on March 14, 2015, because the date was 3/14/15, adding two more digits of pi. The real show-stoppers came a few minutes before 9:30 am and pm, when the first first 10 digits of Pi were represented: 3/14/15 9:26:53.
- There is a style of writing based on Pi. In “Pilish,” the lengths of successive words represent the digits of the number Pi. If you count the letter in each word in this sentence: “How I need a drink, alcoholic in nature, after the heavy lectures involving quantum mechanics!” It’s 3.14159265358979. Mike Keith wrote an entire novel,
*Not a Wake**,*in Pilish. - Some mathematicians think we should celebrate “Tau Day” instead of Pi Day. They argue that Tau (two times pi) is a better circle constant. Tau Day is celebrated on 6/28.
- Pi is named for the Greek letter “p”—it is not named after pie, the dessert treat. But you can use pi to find the volume of a pieor you can use pies to calculate pi.
- If you write the first three digits of pi backwards (3.14) it looks like “PIE.”

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