How to type Iota
To type Iota (ι), press Alt + 953 on Windows, holding Alt while typing the digits on the numeric keypad, or write ι in HTML. On any system you can copy it from this page, or enter its codepoint U+03B9 directly: Ctrl+Shift+U then 03b9 on Linux, or 03b9 then Alt+X in Microsoft Word.
Greek Small Letter Iota
- Copy it
- Unicode
- U+03B9
- Windows
- Alt + 953 needs regedit
| Where | Shortcut | How |
|---|---|---|
| Windows | Alt + 953 | Above 255, so Windows will not accept it as typed. Copy the character instead. |
| Mac | N/A | Press the keys together. |
| HTML | ι | Paste this into HTML source. |
| Unicode | U+03B9 | GREEK SMALL LETTER IOTA |
Other greek symbols
ι lives in the Greek and Coptic block (U+0370-U+03FF), the Greek alphabet, used throughout mathematics and the sciences. Within Unicode it is classified as Ll, a lowercase letter. It has an uppercase counterpart and changes under case conversion. Its bidirectional class makes it left-to-right.
Its uppercase counterpart is Ι (U+0399). They are separate codepoints, so a byte comparison treats them as different characters even though a case-insensitive search does not.
What Iota is used for
In mathematical notation ι is a variable: it stands for a quantity rather than acting on one, so an equation treats it the way it treats x, and the spacing around it is the spacing around a letter. That is the classification unicode-math gives it, and it is what decides how the symbol is set: $\mupiota$ in LaTeX, in maths mode rather than in a sentence.
The command is \mupiota rather than the \iota most people reach for, and the difference is not cosmetic: mup is unicode-math for maths, upright, and this codepoint is the upright letter. Plain LaTeX's short command gives the sloped math-italic letter, which is a different character with a different codepoint. Copying ι into an equation gets you the upright one.
ι is a letter before it is a symbol, and on the Greek keyboard layout it is simply I: the key your keycap already calls I. That is the route when you are typing Greek rather than reaching for one character. How to type Greek on a keyboard has the whole map.
What ι gets confused with
Unicode's own confusables table, the one used to catch lookalike domain names, groups ι with i (U+0069, Latin Small Letter I) and ⅰ (U+2170, Small Roman Numeral One). They are separate characters that render close enough to be mistaken for one another, so a search or a string comparison will separate them where your eye will not. If Iota is not matching where you expect it to, one of these is the usual reason.
What Unicode says about Iota
The code chart points from ι to latin small letter iota (U+0269) and turned greek small letter iota (U+2129). These are the characters the standard thinks you might have meant instead, which makes them the ones worth checking when Iota looks nearly right but not quite.
How Iota behaves in software
ι is East Asian Ambiguous: one column in a Western locale and two in a CJK one. That is why a table that lines up on your machine can break on somebody else's, with no change to the text at all. It is a left-to-right character, so it holds that direction even inside a right-to-left paragraph.
Every way to write Iota
| Form | Value |
|---|---|
| Codepoint | U+03B9 |
| Decimal | 953 |
| UTF-8 bytes | CE B9 |
| UTF-16 bytes | 03 B9 |
| HTML entity | ι |
| HTML numeric | ι or ι |
| CSS | \03B9 |
| JavaScript | \u03B9 |
| Python | \u03B9 |
| URL-encoded | %CE%B9 |
| LaTeX, in maths mode | $\mupiota$ |
| SVG | 03B9.svg · (SIL Open Font License) |
If ι arrives as ι
That is this exact character, undamaged: its two UTF-8 bytes CE B9 are being read one at a time as Windows-1252. The Latin-1 range is where this happens most, because it is the range every legacy system thought it already handled. Nothing is lost, and retyping will not help: the fix is at the reading end, which has to be told the text is UTF-8. An empty rectangle is the opposite complaint, and means the encoding is right and the font has no glyph for U+03B9.