Tau Symbol Copy and Paste (τ Τ)
Small tau (torque)
Unicode U+03C4 · HTML τ · Alt code Alt+231
Tap any symbol to copy it. Each tap also adds it to the box above, so you can copy several together.
Codes for every symbol on this page (Unicode, HTML, Alt, Mac, Word)
| Symbol | Name | Unicode | HTML | Windows Alt code | Mac | MS Word |
|---|---|---|---|---|---|---|
| τ | Small tau (torque) | U+03C4 | τ | Alt+231 | - | 03C4 then Alt+X |
| Τ | Capital tau | U+03A4 | Τ | - | - | 03A4 then Alt+X |
The tau symbol τ is the 19th letter of the Greek alphabet. If you have studied rotation in Class 11 physics, you know it as the torque symbol: the turning effect of a force.
Small τ looks like a T with a curved foot, and capital Τ is identical to the English T. Copy either one from the grid above. Unlike most Greek letters, small tau even has a Windows Alt code, which is explained below.
What Is the Symbol of Torque?
The symbol of torque is τ. Torque measures how strongly a force makes something rotate. Think of opening a heavy door: pushing near the handle (far from the hinges) turns it easily, while pushing near the hinges hardly moves it. The difference is torque.
The formula is:
τ = r F sin θ
- r = distance from the turning point (the pivot)
- F = force applied
- θ = angle between r and F (see the theta symbol)
In vector form it is τ = r × F, a cross product, and its direction follows the right-hand rule.
Torque Symbol in Physics: Worked Example
A mechanic uses a spanner 0.25 m long and pushes at right angles with a force of 40 N.
- Angle θ = 90°, so sin θ = 1.
- τ = 0.25 × 40 × 1 = 10 N m.
- If the mechanic pushes at 30° instead, sin 30° = 0.5, so τ = 5 N m.
That is why a longer spanner, or a push at right angles, makes a stuck nut easier to turn. The unit is the newton metre (N m). Although N m has the same base units as the joule, torque is not written in joules, because it is not energy.
Tau in Electronics: The Time Constant
Outside mechanics, the tau symbol in physics and electronics often means a time constant:
| Circuit | Time constant | What it tells you |
|---|---|---|
| RC (resistor + capacitor) | τ = R C | After one τ, a charging capacitor reaches about 63% of the supply voltage |
| RL (resistor + inductor) | τ = L ÷ R | How fast the current builds up |
Example: R = 10 kΩ and C = 100 µF give τ = 10,000 × 0.0001 = 1 second. After about 5τ the capacitor is treated as fully charged. For Ω and µ, see the ohm symbol and micro symbol pages.
Other uses of τ: shear stress in strength of materials, mean lifetime of a radioactive nucleus, and the tau particle, a heavy cousin of the electron.
How to Type the Tau Symbol
- Windows Alt code: hold Alt and type 231 on the number pad (Num Lock on). This comes from the old DOS character table, so a few apps may show a different character. If that happens, use the Word method.
- Word: type
03C4, then Alt+X. For capital Τ, use03A4. - Google Docs: Insert > Special characters, search "tau".
- Mac: there is no Option shortcut; use Character Viewer (Control+Command+Space).
- HTML:
τ.
Note that Alt+231 and Alt+0231 are different: Alt+0231 gives ç (c with cedilla), not tau.
Tau and 2π: A Friendly Maths Debate
Some mathematicians suggest using τ for 2π ≈ 6.283, the number of radians in a full circle. Their point: a full turn would be τ, a half turn τ/2, and a quarter turn τ/4, which they find more natural. Most textbooks and exams still use π, so in school always write 2π. Read about π on the pi symbol page, and see every Greek letter on the Greek letters page.
Frequently asked questions
What is the symbol of tau?
The symbol of tau is τ (small) and Τ (capital). The small letter is the one used in physics and engineering.
What is the symbol of torque in physics and its SI unit?
The symbol of torque in physics is τ and its SI unit is the newton metre (N m). Some older books also write torque as M or T, especially in engineering mechanics.
How is tau pronounced?
In English it is usually said like "taw" or to rhyme with "cow". In modern Greek it is "taf". Any of these will be understood in class.
Is torque a vector?
Yes. Torque has both size and direction. Its direction is along the axis of rotation, found with the right-hand rule.
Why does my Alt+231 give a different character?
Alt codes without a leading zero use the old DOS table, and a few programs handle them differently. If τ does not appear, type 03C4 then Alt+X in Word, or copy τ from this page.