What does "Pi" mean?

yeah, i know it equals 22/7 and is used to find the diameter and area of circles, but why do they call it “pi”? does it have some foreign meaning (kinda like “sophomore” means “wise fool”)? or was it named after someone? or was someone just soo hungry trying to analyze their round pastry that they left off the e?

A guess:

It’s the name of the symbol. Just like H is called “aitch”.

Pi is the Greek letter pi: p. I’m not sure why they chose that particular Greek letter, though.

BTWQ, it’s not equal to 22/7, it’s only approximately equal to that. Pi is irrational, which means it can not be represented by a simple fraction.

It’s Greek for “1920s style death ray.”

Seriously … you know how a pie is round? Well, the powers that got it from there. Before there were pies, pi was called “circumnaviflex.”


Pi is the Greek letter represented by… well… the pi symbol. As far as I know, somebody just designated it to represent the number you get when you divide the circumference of a circle by its diameter. Just so they wouldn’t have to write D/C all the time - esp. if you were trying to find one of the two!

And for the record, 22/7 is only a rough approximation. It’s only equal to pi to the second decimal place (3.14).

A better approximantion would be 3.141592654.

Or better still:
3.141592653589793238462 6433832795028841971693 9937510582097494459230 7816406286208998628034 8253421170679821480865 132823066470938446


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Then there’s One Million Digits of Pi for those who need extreme accuracy. If you knew the exact diameter of an Earth-sized circle, this many digits would allow you to calculate the circumference to within less than the width of an atom.

Anything you can do…

141592653589 793238462643 383279502884 197169399375 105820974944 592307816406 286208998628 034825342117 067982148086 513282306647 093844609550 582231725359 408128481117 450284102701 938521105559 644622948954 930381964428 810975665933 446128475648 233786783165 271201909145 648566923460 348610454326 648213393607 260249141273 724587006606 315588174881 520920962829 254091715364 367892590360 011330530548 820466521384 146951941511 609433057270 365759591953 092186117381 932611793105 118548074462 379962749567 351885752724 891227938183 011949129833 673362440656 643086021394 946395224737 190702179860 943702770539 217176293176 752384674818 467669405132 000568127145 263560827785 771342757789 609173637178 721468440901 224953430146 549585371050 792279689258 923542019956 112129021960 864034418159 813629774771 309960518707 211349999998 372978049951 059731732816 096318595024 459455346908 302642522308 253344685035 261931188171 010003137838 752886587533 208381420617 177669147303 598253490428 755468731159 562863882353 787593751957 781857780532 171226806613 001927876611 195909216420199

Dang - on preview I see you’ve linked to a million digits (the above is one thousand).
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Here’s a quote that says who first ‘coined’ the notation, but good luck finding out exactly why he used the letter pi.

From here.

Everything you ever wanted to know about pi, courtesy of bibliophage.

And Q.E.D., you’ve just barely scratched the surface of how ridiculous a million digits of pi is. If you had a circle the size of the known Universe, and wanted to measure it to within a Planck length, you’d only need about 61 digits of pi. I can’t even think of an analogy that comes anywhere close to describing what sort of situation you’d use a million digits in.

The circumference of a circle is the perimeter of the circle; pi is the first letter in the Greek word for perimeter, and apparently that’s why the letter pi is the symbol used for the constant:


For a more accurate ratio approximation, remember “11 33 55”, then split it down the middle. Pi is very close to 355/113: 3.14159292, or only 0.0000085% off.

Yeah, I know, but I didn’t feel like working out the exact precision. Maybe I’ll get bored and work out some interesting analogy. Something involving twinkies.

As I say in the Staff Report linked to by Chronos, pi (the Greek equivalen of p) was used by Oughtred in 1647 to stand for the English word “periphery.” It was used in the context of discussing the ratio we now call pi, but he used it to represent not the ratio itself, but what we now call the circumference. The first writer to use the letter to represent the ratio itself was Jones in 1706. Euler popularized the notation starting in 1736.

As I say in the Staff Report What’s the origin of “sophomore”?, the “wise fool” interpretation is folk etymology. “Sophomore” is really a variant of “sophist.”

In 1706, William Jones looked at a pie his wife had just baked (an apple pie, in fact, in honor of Isaac Newton), and wondered what was the ratio of the of the circumference to the diameter of the pie. When he worked it out to several decimal places, he ate the final piece and named the value in honor of that delicious repast. And now you know.

The circumference of a circle is always 3.1415926… times longer than its diameter.

That’s what pi is. If we all agree to call it Matilda tomorrow, it changes only in name.


Pi r round, cornbread r square.

Thank you, and good morning.

And Cecil’s column: How do scientists go about calculating pi to umpteen decimal places?

As Cecil says, quoting a learned treatise, “thirty-nine places of pi suffice for computing the circumference of a circle girdling the known universe with an error no greater than the radius of a hydrogen atom.”

It would be rude not to mention our good friends in Indiana, who thoroughly examined the issue of pi.

Did a state legislature once pass a law saying pi equals 3?