Pi symbol
The pi symbol π is the most famous letter in mathematics: the ratio of a circle’s circumference to its diameter, the same for every circle that has ever existed — about 3.14159, with decimals that never end and never repeat. Copy π and its capital Π here, with the formulas they live in and the story of the never-ending number.
Copy pi
Pi at work, ready to copy
π or Π — lower or upper?
| Form | The job |
|---|---|
| π (lowercase) | The constant 3.14159… — circles, angles in radians (π rad = 180°), waves and probability |
| Π (uppercase) | The product operator: multiply a whole series together, the way Σ adds one — a different symbol wearing the same letter |
| ϖ (variant) | An old cursive pi shape, kept for astronomy’s perihelion symbol and vintage texts |
The letter was chosen in 1706 by William Jones from the Greek word for perimeter, and Euler made it universal. The number itself is far older: Archimedes trapped it between polygons around 250 BC, and computers have now chased its decimals past a hundred trillion places — a hunt with no finish line, because π is irrational: its decimals truly never settle into a pattern.
How to type it
| Platform | Method |
|---|---|
| Windows (Word) | Type 03C0 then Alt + X (03A0 for Π) |
| Mac | Option + P on some layouts gives π; otherwise Character Viewer, search “pi” |
| HTML / LaTeX | HTML: the “pi” entity name (ampersand + pi;) or code 960. LaTeX: \pi and \Pi |
| Excel / Sheets | The PI() function returns the value; for the character in a label, copy π from here |
Explore more
Pi’s operator siblings live with the math symbols, its letter family is the Greek alphabet, and the other great constant’s partner sign is the root symbol it so often travels with.
Frequently asked questions
What is the value of pi?
Approximately 3.14159265359 — circumference divided by diameter, for any circle. School work usually uses 3.14 or the fraction 22/7; engineering uses more decimals; nobody uses them all, because there are infinitely many.
Why is pi an infinite number?
Pi is irrational: it cannot be written as a simple fraction, so its decimal expansion never ends and never repeats. That was proven in the 1760s by Lambert — the decimals are not just long, they are provably endless.
What is Pi Day?
March 14 — written 3/14 in US format, matching pi’s first digits. Schools, bakeries and maths departments celebrate with circular pies, which is the correct unit of appreciation for a circle constant.
Is Π the same as π?
Same Greek letter, different mathematical job. Lowercase π is the constant. Capital Π is an operator meaning “multiply everything in this series” — the multiplication twin of Σ, which adds. Context and size tell them apart at a glance.