Eta — η Greek Letter Symbol
η
Eta — η / Η
7th letter of the Greek alphabet · pronounced /ˈiːtə/
PhysicsEngineeringThermodynamicsFluid Mechanics
Copy symbol
η
Lowercase eta
Η
Uppercase Eta
Technical reference
| Unicode (lowercase) | U+03B7 |
| Unicode (uppercase) | U+0397 |
| HTML entity | η |
| HTML decimal | η |
| LaTeX | \eta |
| Python / Unicode escape | \u03b7 |
| Alt code (Windows) | Alt + 951 |
Uses in science & engineering
Efficiency
Ratio of useful output to total input energy. Used across thermodynamics, electrical, and mechanical engineering.
\(\eta = \frac{W_{out}}{W_{in}}\)
Dynamic viscosity
Resistance of a fluid to flow. Fundamental property in fluid mechanics and hydraulics.
\(\tau = \eta \frac{du}{dy}\)
Intrinsic impedance
Ratio of electric to magnetic field in an electromagnetic wave propagating through a medium.
\(\eta = \sqrt{\frac{\mu}{\varepsilon}}\)
Carnot efficiency
Maximum theoretical efficiency of a heat engine operating between two temperatures.
\(\eta_{Carnot} = 1 – \frac{T_C}{T_H}\)
Related symbols
How to insert in applications
Windows
Best option: copy from this page.
Or press Win + . to open emoji & symbols panel.
Alt codes work only in Word/Notepad with NumLock on and English layout — not in browsers.
Or press Win + . to open emoji & symbols panel.
Alt codes work only in Word/Notepad with NumLock on and English layout — not in browsers.
macOS
Press ⌃⌘Space → Character Viewer → search “eta”
Microsoft Word
Type 03b7 then press Alt+X
Google Docs
Insert → Special characters → search by name
Excel
Insert → Symbol → Subset: Greek → select symbol
LaTeX
Use in math mode: $ … $
Python
Use Unicode escape or chr()
HTML / CSS
Use HTML entity or decimal code