The symbol

The Pi Symbol: π

π is the sixteenth letter of the Greek alphabet, and for the last three centuries it has been mathematics' shorthand for the ratio of a circle's circumference to its diameter. Here's how to copy it, type it, and understand where it came from.

Copy: π (U+03C0)

What the π symbol is

The symbol π is the lowercase Greek letter pi, pronounced "pie" in English (and closer to "pee" in modern Greek). In mathematics it almost always stands for one specific constant: the number 3.14159265…, the ratio you get when you divide any circle's circumference by its diameter. That value is the same for every circle, which is exactly why it deserves a single, permanent symbol instead of being written out longhand every time.

It's worth being precise about one thing: the letter π is just a name. The number it points to is irrational and endless, but the symbol itself is a tidy single character you can drop into an equation, a spreadsheet, or a text message.

Unicode and HTML entity

On computers, the lowercase pi symbol lives at Unicode code point U+03C0. That's the canonical way to refer to it in any system that speaks Unicode, which today is nearly all of them.

Named HTML entity: π
Numeric HTML entity: π (960 is 0x03C0 in decimal)
CSS / JavaScript escape: \03C0 and π respectively

All three render the same character: π. If you're writing a web page and want the symbol to survive copy-paste and encoding mishaps, the entities are a safe bet.

How to type the pi symbol

Copying from the card above is the quickest route, but every major platform can produce π directly from the keyboard.

Windows: Hold Alt and type 227 on the numeric keypad, then release. Alternatively, in most Windows apps you can type 03C0 and immediately press Alt+X to convert the code into the symbol.
Mac: Press Option+P. That's it — one keystroke, no keypad required.
iPhone & iPad: The default keyboard has no pi key, so the easy path is to copy π once and let autocorrect or your text-replacement shortcuts remember it. You can also add a keyboard shortcut in Settings → General → Keyboard → Text Replacement that expands, say, "ppi" into π.
Android: Switch to the symbols layer, or long-press keys on a Greek-enabled keyboard such as Gboard with the Greek language added. Copy-paste works everywhere as a fallback.
LaTeX: Simply write \pi in math mode. The capital is \Pi. This is how virtually every math paper in the world sets the symbol.
Microsoft Word: Type 03C0 and press Alt+X, or use Insert → Symbol and pick the Greek block. Inside an equation field, typing \pi followed by a space also works.

Lowercase π versus capital Π

The two are not interchangeable. Lowercase π (U+03C0) is the circle constant. The capital Π (U+03A0) means something completely different: it's the product operator, the multiplication cousin of the summation sign Σ. When you see Π stretched large with limits above and below it, it's telling you to multiply a sequence of terms together, not to divide a circle. Mathematicians rely on the case distinction constantly, so it pays to reach for the right one.

A short history of the symbol

Pi the number is ancient — Babylonian and Egyptian scribes were approximating it nearly four thousand years ago — but pi the symbol is comparatively young. The Welsh mathematician William Jones was the first to use π for this specific ratio, in his 1706 book Synopsis Palmariorum Matheseos. Before that, people wrote the ratio out as a phrase or used other letters.

Jones's choice might have stayed a footnote if not for Leonhard Euler, the most influential mathematician of the eighteenth century, who adopted π in his enormously popular writings from the 1730s onward. Once Euler used it, everyone used it. The letter itself was a natural pick: π is the first letter of the Greek words περιφέρεια (periphery) and περίμετρος (perimeter) — the very thing you measure when you walk around a circle.