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What is pi (π)?
Quick answer
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. π = a circle's circumference divided by its diameter, ≈ 3.14159.
Key things to understand
- π = a circle's circumference divided by its diameter, ≈ 3.14159.
- It's the same for every circle, no matter the size.
- It's 'irrational' — its decimals never end or repeat.
- It appears far beyond circles, throughout math and physics.
People also ask
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.