Pi (π) is an irrational, transcendental number meaning it has infinite non-repeating decimal places. It appears throughout mathematics, physics, and engineering.
Key Values
π ≈ 3.14159265358979... Common approximations: 22/7 or 355/113 (accurate to 6 decimal places).
Where π Appears
- Circle area: A = πr²
- Circumference: C = 2πr
- Sphere volume: V = (4/3)πr³
- Normal distribution: (1/√(2π))e^(−x²/2)
- Euler's identity: e^(iπ) + 1 = 0
How Precisely Do We Actually Need Pi?
NASA uses only 15–16 digits of pi (3.14159265358979) for its most precise interplanetary navigation calculations — enough to calculate a circle the size of the observable universe to within the width of a single hydrogen atom. Computing pi to trillions of digits, a popular computational benchmark, has no practical scientific application beyond testing computer hardware and algorithms.
Pi Day
March 14 (3/14 in U.S. date format) is celebrated globally as Pi Day, chosen for matching pi's first three digits. It was officially recognized by the U.S. House of Representatives in 2009 and is widely celebrated in math classrooms with pie-eating and recitation contests.