Theta Symbol (θ, Θ): Angles, Big-Theta and LaTeX
July 1, 2026
The theta symbol is θ in lowercase and Θ in uppercase. Lowercase θ is the default name for an angle in almost every branch of maths and physics. Uppercase Θ means Big-Theta in computer science, and temperature in some engineering conventions. Copy either below, or jump to how to type it.
| Character | Unicode | HTML entity | LaTeX | Windows alt code |
|---|---|---|---|---|
| θ lowercase theta | U+03B8 | θ | \theta | — |
| Θ uppercase theta | U+0398 | Θ | \Theta | Alt + 233 |
What the symbol means
| Where | Meaning |
|---|---|
| Trigonometry | The angle in sin θ, cos θ, tan θ |
| Polar coordinates | The angular coordinate, paired with radius r |
| Physics | Angle of incidence, phase angle, angular displacement |
| Computer science | Big-Theta — a tight asymptotic bound, both upper and lower |
| Statistics | θ conventionally denotes an unknown parameter |
| Engineering | Θ is sometimes temperature, and the SI dimension symbol |
θ as an angle
If a maths problem has an unnamed angle, it is θ by convention. The trigonometric identities are all written in terms of it, and radians rather than degrees are assumed unless a degree sign says otherwise.
Both of those arc formulas only hold when θ is in radians. In degrees you need an extra factor of π/180 — a very common source of wrong answers.
θ in polar and spherical coordinates
Polar coordinates name a point by distance and angle instead of x and y. Be careful in three dimensions: physics and maths swap the meanings of θ and φ, so always check which convention a text is using before trusting a formula.
Θ as a tight bound
In algorithm analysis the three bounds form a set: Big-O is an upper bound, Big-Omega a lower one, and Big-Theta says both hold — the growth rate is pinned from above and below. Saying an algorithm is Θ(n log n) is a stronger claim than O(n log n).
How to type it
Windows
- Uppercase Θ: hold
Altand type233on the numeric keypad - Lowercase θ has no legacy alt code. In Word, type
03B8and pressAlt + X - Elsewhere, press
Windows + .and search “theta”
Mac
- Open Character Viewer with
Control + Command + Spaceand search “theta” - Or enable the Greek keyboard, where θ sits on the
ukey
HTML
θorθfor θΘorΘfor Θϑfor the variant ϑ
In LaTeX
There are two lowercase forms. \theta is the usual one; \vartheta is the curly variant, useful when a document needs two distinct angles that would otherwise collide.
Use ^\circ for the degree sign in maths mode — 45^\circ, not 45°. The literal character will not match the surrounding font in most classes.
Frequently asked questions
What does θ mean in maths?
An angle, nearly always. It is the default name for an unknown or variable angle, in radians unless a degree sign says otherwise.
What is the difference between θ and Θ?
Case. Lowercase θ is an angle. Uppercase Θ is Big-Theta notation in computer science, or a temperature in some engineering conventions.
What is ϑ?
The variant form of lowercase theta (U+03D1, \vartheta). It means the same letter — use it when you need two visually distinct thetas in one document.
See also the alpha symbol, omega symbol and lambda symbol.
Try it free
Save an afternoon on your next paper.
Turn handwritten working into submission-ready LaTeX in seconds — θ, φ, subscripts and all — so you spend the time on the analysis instead.
Convert your paper
Empowering students and researchers with AI-powered tools for academic writing.
Go to appContact us© 2026 Underleaf. All rights reserved.