Tau in LaTeX (\tau)

Where it is used

Lowercase Greek tau, used for time constants, torque, proper time, and Kendall's rank correlation.

Physics writes torque as \boldsymbol{\tau} = \mathbf{r} \times \mathbf{F}, a time constant in e^{-t/\tau}, and proper time \tau in relativity. Statistics has Kendall's \tau, and some authors use \tau = 2\pi as a circle constant. Number theory uses \tau(n) for the number of divisors, and modular forms use \tau for a point in the upper half-plane. Type theory often writes types as \tau and \sigma. There is no \Tau command, since capital tau equals Latin T. In some fonts \tau resembles a small t, so pick distinct names for nearby variables.

Minimal compilable example

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

\documentclass{article}
\begin{document}
Tau: $\tau$

\[ V(t) = V_0\, e^{-t/\tau}, \quad \tau = RC \]
\end{document}

Related symbols

• Upsilon\upsilon
• Sigma (Upper)\Sigma
• Upsilon (Upper)\Upsilon
• Sigma\sigma
• Phi\phi
• Rho\rho

Frequently asked questions

How do I write Tau in LaTeX?

Type \tau in math mode, for example $V(t) = V_0\, e^{-t/\tau}, \quad \tau = RC$. It works in plain LaTeX without loading any package.

Which package do I need for \tau?

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

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

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