τ
τ Tau Symbol
Tau (τ) is the 19th Greek letter — torque in physics, the time constant in engineering, and Kendall's rank correlation in statistics.
Also known as: tau symbol, torque symbol, tau greek letter, time constant symbol.
Codes
| Symbol | τ | |
| Uppercase | Τ · U+03A4 | |
| Unicode | U+03C4 | |
| HTML entity (named) | τ | |
| HTML entity (decimal) | τ | |
| HTML entity (hex) | τ | |
| CSS | \03C4 | |
| LaTeX | \tau | |
| Windows Alt code | Alt + 231 |
How to type τ (Tau Symbol)
WindowsAlt + 231
Hold Alt and type 231 on the numeric keypad, then release Alt (or type 03C4 then Alt + X in Word).
Mac
No default keystroke. Open Character Viewer (Control + Cmd + Space) and search “tau”, or copy τ above.
Microsoft Word03C4, Alt + X
Type 03C4, then press Alt + X to convert it to τ.
Google Docs
Insert → Special characters, then search “tau” or “greek small letter tau”.
LaTeX\tau
Use \tau in math mode (\Tau is not defined — the uppercase Τ is just a Latin T shape, so write T).
Usage
- In physics τ is torque, the rotational analogue of force: τ = r × F.
- In engineering τ is the time constant of a system — after time τ, an exponential decay has fallen to about 37% of its starting value.
- In statistics, Kendall's τ measures rank correlation, an alternative to Pearson's r when the data are ordinal.
- Unlike μ, tau's Alt code is safe. Alt + 231 gives the genuine Greek letter τ (U+03C4). Compare μ, where Alt + 230 gives the micro sign µ (U+00B5) — a different character that only looks like the Greek mu. Tau has no such twin.