## What is pi?

Pi is a number that is just a little bigger than 3.14. It is the number you get if you divide the circumference of any circle by its diameter. It’s the same for all circles. You can approximate pi for yourself by taking some circular things like the tops of jars and CD’s and frisbees and measuring their diameter and their circumference. When you divide the circumference by the diameter, you’ll get an answer something like 3.14. It will be the same every time (unless you measured wrong).

## Pi is an irrational number

Actually, 3.14 is only approximately equal to pi. That’s because pi is an irrational number. That means that when you write pi as a decimal it goes on forever, never ending and never repeating itself. The first six digits of pi are 3.14159, and that’s all you need for most practical purposes. In most cases just 3.14 is enough.

## A million digits of pi

Check out this webpage with a million digits of pi.

## Why is this number called pi? History of pi

Usually in math we write pi with the Greek letter π, which is the letter “p” in Greek. You pronounce it “pie”, like apple pie. It is called pi because π is the first letter of the Greek word “perimetros” or perimeter. But it was not the Ancient Greeks who first discussed the value of pi. Mathematicians in the Babylonian Empire, about 2000 BC, had already figured out that pi was about 25/8, or 3.125. By about 1700 BC, in the Middle Kingdom, Egyptian mathematicians calculated pi to be about 3.16. Archimedes calculated that π was a little bigger than 3.1408. People have been gradually getting closer ever since, with early contributions from mathematicians working in China, India, and the Islamic Empire. By 263 AD, the Chinese mathematician Liu Hui had calculated that pi was 3.141.

## Learn by doing: circumference of a circle

More about Circles

## Bibliography and further reading about pi:

JustineSeptember 30, 2018 at 10:07 pmWhat is the Center Pi? Anyone knows the answer?

za dank memesMarch 16, 2018 at 7:09 amza

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very nice!

emilyMarch 14, 2018 at 11:34 ampi is equal to 3.14

Karen CarrMarch 14, 2018 at 12:34 pmNo, it’s not. Pi is approximately 3.14, but it is an irrational number that continues infinitely, more and more decimals, forever, without repeating itself. A more accurate number is 3.1415923, but even that is only an approximation good enough for most practical purposes.

bobettMarch 14, 2018 at 11:04 amhow do you get the area of pi

Karen CarrMarch 14, 2018 at 11:15 amAre you looking for this page? https://quatr.us/math/proof-area-circle.htm

bobMarch 14, 2018 at 9:23 amthis was very helpful what sa do

Karen CarrMarch 14, 2018 at 9:40 amI’m glad we could help!