Theta in LaTeX (\theta)

Where it is used

Lowercase Greek theta, the usual name for angles and for model parameters in statistics and ML.

Trigonometry and polar coordinates use \theta for angles, as in (r\cos\theta, r\sin\theta). Statistics and machine learning use it for parameter vectors, with \hat{\theta} for an estimator and \theta^* for the optimum. Big-Theta complexity bounds use the uppercase \Theta, not \theta. The variant \vartheta is a script-like form occasionally used for a second angle or in physics. When writing an estimator, \hat{\theta} keeps the hat centered better than \widehat{\theta}, which is meant for wider arguments. In Bayesian notation, \theta also names the unknown quantity in the posterior p(\theta \mid x).

Also listed under: Trigonometry, Machine Learning & AI

Minimal compilable example

Paste this into an empty .tex file and compile it with pdfLaTeX, XeLaTeX or LuaLaTeX.

\documentclass{article}
\begin{document}
Theta: $\theta$

\[ \hat{\theta} = \arg\max_{\theta} \log p(x \mid \theta) \]
\end{document}

Related symbols

• Theta (Upper)\Theta
• Eta\eta
• Iota\iota
• Zeta\zeta
• Kappa\kappa
• Epsilon (Variant)\varepsilon

Frequently asked questions

How do I write Theta in LaTeX?

Type \theta in math mode, for example $\hat{\theta} = \arg\max_{\theta} \log p(x \mid \theta)$. It works in plain LaTeX without loading any package.

Which package do I need for \theta?

None. \theta is part of standard LaTeX, so it compiles with nothing in the preamble but the document class.

Can I use \theta in text mode, or only in math mode?

Only in math mode. Outside $...$ LaTeX stops with "Missing $ inserted", so write $\theta$ in running text. If you only need the glyph in text, paste the Unicode character θ instead (with XeLaTeX or LuaLaTeX and a font that has it).