Pi is the most famous number in mathematics and one of the most mysterious. How much do you actually know beyond 3.14?
This quiz is not just about memorising digits. It is about understanding why pi is everywhere in mathematics, why it never ends and why that matters.
Pick your level
Pi (π) is the constant ratio of a circle's circumference to its diameter: approximately 3.1415925358979... and then infinitely more, without ever repeating. Mathematicians have been chasing its digits for 4,000 years, from the Babylonians to Archimedes in ancient Syracuse to Google's 100 trillion digits in 2022. Pi is irrational (never repeating) and transcendental (impossible to express as any algebraic equation with integer coefficients).
Pi Day is celebrated on 14 March (3/14 in American date format), which also happens to be Albert Einstein's birthday. The classic English mnemonic "How I wish I could calculate pi" encodes the first seven digits: count the letters in each word and you get 3.141592. This quiz goes well beyond that.
All ten easy level questions, with the answer and the reasoning behind it.
Correct answer: The circle
The circle, whatever its size.
Correct answer: 3.14
3.14, the classic school value.
Correct answer: 4
4, in 3.14.
Correct answer: It is twice it
Twice it, going right across instead of stopping at the centre.
Correct answer: Albert Einstein
Albert Einstein, born in 1879.
Correct answer: π × d
π × d, which is more or less the definition of pi.
Correct answer: Pie
Pie, in round tins, and strongly recommended.
Correct answer: 3.1
3.1, because the next digit is 4.
Correct answer: Life of Pi
Life of Pi, whose hero has his own reasons for preferring that nickname.
Correct answer: 6.28
6.28, a value some people prefer to call tau.
Want to warm up before playing or double-check something? Open any question to reveal the correct answer and a short explanation.
Correct answer: 14159
Pi equals 3.1415925358979... The first 5 decimal digits are 1, 4, 1, 5, 9. A classic English mnemonic is "How I wish I could calculate pi" where each word's letter count gives a digit: 3.141592...
Correct answer: In American notation, 3/14 matches the first 3 digits of pi
14 March is written as 3/14 in American notation (month/day), which mirrors the first digits of pi (3.14). It is also the birthday of Albert Einstein, born on 14 March 1879.
Correct answer: pi x r²
The area of a circle is pi x r² (pi multiplied by the square of the radius). The circumference is 2 x pi x r (or pi x d, where d is the diameter). These are the two most commonly used formulas involving pi.
Correct answer: Irrational and transcendental
Pi is both irrational (its decimal digits never terminate or repeat) and transcendental (it cannot be a solution to any polynomial equation with integer coefficients). Pi's transcendence was proved by Ferdinand von Lindemann in 1882.
Correct answer: Archimedes
Archimedes of Syracuse (287-212 BC) established that pi lies between 223/71 and 22/7 (between 3.1408 and 3.1428) by inscribing 96-sided polygons inside and around a circle. His method was the standard reference for centuries.
Correct answer: How I wish I could calculate pi
"How I wish I could calculate pi" is a classic English mnemonic: the number of letters in each word gives the digits 3.141592... Other mnemonics exist, including "May I have a large container of coffee" (3.141592...).
Correct answer: Over 300 trillion
The record passed 300 trillion digits in 2025, after Google's 100 trillion in 2022. These records keep being broken but have no practical use beyond around ten digits for most real-world applications.
Correct answer: Euler
Leonhard Euler (1707-1783) popularised the use of the symbol pi in his writings from 1737, making the notation universal. The letter pi had previously been used by William Jones in 1706, but it was Euler who standardised it.
Correct answer: (4/3) x pi x r³
The volume of a sphere is (4/3) x pi x r³. The surface area of a sphere is 4 x pi x r². These formulas are fundamental in three-dimensional geometry and both involve pi.
Correct answer: 355/113
The fraction 355/113 is a remarkably accurate approximation of pi, equalling approximately 3.14159292, with an error of less than 3 ten-millionths. It was discovered by Chinese mathematician Zu Chongzhi in the 5th century.
Stuck on one, or just curious how nasty it gets? Every hard mode question is here with its answer and the reasoning behind it.
Correct answer: 2
2, as pi begins 3.141592.
Correct answer: Stephen Hawking
Stephen Hawking, on Einstein's birthday as it happens.
Correct answer: Tau
Tau, whose fans have their own Tau Day on 28 June.
Correct answer: Squaring the circle
Squaring the circle with only a compass and straightedge.
Correct answer: William Shanks
William Shanks. The mistake was only spotted in 1945.
Correct answer: Buffon's needle
Buffon's needle, from the 18th-century French naturalist.
Correct answer: π²/6
π²/6, the Basel problem, solved by Euler in 1734.
Correct answer: The Chudnovsky algorithm
The Chudnovsky algorithm, published in 1988.
Correct answer: Piphilology
Piphilology, in which word lengths match the digits.
Correct answer: The Rhind Papyrus
The Rhind Papyrus, written about 1550 BC.