Lowercase theta θ is the eighth Greek letter. Type 03B8 then Alt+X in Word. It is the default name for an angle in trigonometry and geometry, and it also names a parameter in statistics and machine learning.
01 All shortcuts at a glance
| Platform | Shortcut | |
|---|---|---|
| Windows (any app) | Win+. or Win+; emoji/symbol picker, or Character Map (Win+R → charmap) |
|
| Mac | Control+Command+Space to open Character Viewer, search "Greek Small Letter Theta" |
|
| Word / Outlook | Type 03B8, then press Alt+X |
|
| Linux (IBus) | Ctrl+Shift+U, then 03b8, then Enter |
|
| HTML / CSS | θ · \03b8 (CSS) |
02 Step by step, per platform
A real, followable procedure for every platform, not a thin restatement of the shortcut.
Windows
- Open Character Map: Win+R, type charmap, press Enter.
- Search or scroll for Greek Small Letter Theta (U+03B8).
- Select it, click Copy, then paste where you need it.
Mac
- Press Control+Command+Space to open the Character Viewer.
- Type "Greek Small Letter Theta" in the search field.
- Double-click the result to insert it.
Microsoft Word
- Type 03B8.
- Press Alt+X immediately after, it converts the hex code to θ.
03 Characters in this set
04 Troubleshooting & confusables
| Looks like it | But it's actually | When to use |
|---|---|---|
| ϑ (U+03D1) | Greek theta symbol, a cursive variant | A stylistic variant used in some texts for a second theta-like quantity. |
| ø (U+00F8) | Latin small o with stroke | A Danish and Norwegian letter. The stroke crosses the whole circle, unlike theta. |
| Θ (U+0398) | Greek capital theta | In computer science it denotes a tight asymptotic bound, distinct from big O. |
05 FAQ
What is the Unicode code point for theta?
Lowercase theta is U+03B8 and the capital is U+0398. The cursive variant is a separate character at U+03D1.
Why is θ used for angles?
It is a long-standing convention rather than a rule, dating to early trigonometric writing. Once established it became the default, with φ and ψ as the next choices.
What does Θ mean in computer science?
Capital theta gives a tight bound on an algorithm's growth, meaning it is bounded both above and below. Big O gives only an upper bound, so Θ is the stronger statement.
How is it different from ø?
The Danish and Norwegian ø has a stroke crossing the entire letter and extending past it. Theta's bar sits inside the oval. They are unrelated characters in different scripts.
What does θ mean in machine learning?
It is the conventional name for the set of parameters a model learns. Training is described as finding the θ that minimises a loss function.