Pi

Pi is a very famous number in math. It is about 3.14. Pi helps us work with circles. It tells us how the edge of a circle compares to the line across the middle. People have known about pi for thousands of years.

What Is Pi?

Pi is a number you get when you measure a circle. Take the distance around the circle. Then divide it by the distance across the middle. You always get pi. This is true for any circle, big or small. Pi starts with 3.14, but the numbers after go on forever.

A circle unrolls to show how pi measures the way around.
A circle unrolls to show how pi measures the way around. (John Reid / Wikimedia Commons)

Why Pi Is Special

Pi never ends and never repeats. This makes it very unusual. We use a Greek letter to write pi. It looks like this. Pi is used in math, science, and building things. It helps people make wheels, clocks, and even send rockets to space.

Fun Facts

  • Pi Day is on March 14 because the date looks like 3.14.
  • People have found more than 60 trillion digits of pi using computers.
  • Albert Einstein was born on Pi Day in 1879.

Did You Know?

Some people try to memorize as many digits of pi as they can. The world record is over 70,000 digits!