Mathematics
What is Pi (π)?
Pi (π) is the ratio of a circle's circumference to its diameter — about 3.14159. It's the same for every circle, and its digits go on forever without repeating, making it one of math's most famous constants.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains pi (π).
Key things to understand
- 1π = a circle's circumference divided by its diameter, ≈ 3.14159.
- 2It's the same for every circle, no matter the size.
- 3It's 'irrational' — its decimals never end or repeat.
- 4It appears far beyond circles, throughout math and physics.
Frequently asked questions
- What is pi used for?
- Calculating circles and spheres (circumference, area, volume) and across geometry, physics, and engineering.
- Why does pi never end?
- It's an irrational number, so its decimal expansion is infinite and non-repeating.
- What is the value of pi?
- Approximately 3.14159, though it continues infinitely.