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Pi Approximation Day

Fun · July 22

Pi Approximation Day honors 22/7, the handy fraction that stands in for pi, the ratio of a circle's circumference to its diameter.

Pi Approximation Day falls on Thursday, July 22, 2027. That is 268 days away.

Pi is the number you get when you divide any circle's circumference by its diameter. It starts 3.14159 and never settles into a repeating pattern, which makes it awkward to write down in full. Pi Approximation Day, also called Casual Pi Day, honors the shortcut: the fraction 22/7.

Divide 22 by 7 and you get about 3.142857. That is a little larger than pi, but close enough that students, carpenters and anyone sketching a round garden bed have leaned on it for a long time. It is easy to remember and easy to work with by hand, which is most of what you want from a number you did not choose.

The day has a relaxed feel. People bake pies, of course, since the pun is hard to resist. Others measure things around the house with a piece of string and a ruler, wrapping the string around a mug or a lid, then dividing by the width to see how close they land. Results tend to wobble near 3.1, and the wobble is part of the charm.

There are other approximations too. The fraction 355/113 is far more accurate, matching pi to six decimal places, though it is harder to keep in your head. Comparing the two is a nice way to see the trade between precision and convenience.

Plenty of everyday math runs fine on 22/7, from the edge of a pizza to the rim of a bicycle wheel.

Ways to celebrate

• Measure a round object with string and divide by its width.
• Bake or share a pie, sliced into seven pieces.
• Compare 22/7 and 355/113 against pi on a calculator.
• Teach a child how to find a circle's circumference.

Dates

All national days on July 22

Also on July 22

• National Hammock Day
• National Mango Day
• National Penuche Fudge Day
• Spoonerism Day
• National Ratcatcher's Day

Categories: Fun days