Greek Alphabet Reference
All 24 Greek letters with names and where each is used in math and science.
Click any letter to copy it.
The Greek alphabet has 24 letters, from alpha to omega. Each has an uppercase and lowercase form, and many stand for fixed ideas in math and science — π for the circle constant, Σ for a sum, σ for standard deviation, λ for wavelength, and θ for an angle.
The alphabet of science
Greek letters fill the gaps the Latin alphabet leaves: π for a constant, Σ for a sum, λ for wavelength, σ for standard deviation. The table above lists all 24 letters with both cases and their common uses — click any one to copy it. Below is the context that makes them stick.
Why case carries meaning
Upper and lower case are not interchangeable in notation. Capital Σ is a summation while lowercase σ is standard deviation; capital Δ is a finite change while lowercase δ is an infinitesimal one; capital Φ and lowercase φ often stand for different angles or potentials. Always copy the case the formula actually uses.
Letters you will meet most
The handful of Greek letters that dominate math, physics, and statistics.
| Letter | Name | Typical meaning |
|---|---|---|
| π | pi | Circle constant, 3.14159… |
| Σ / σ | sigma | Summation / standard deviation |
| Δ / δ | delta | Change / small change |
| λ | lambda | Wavelength, eigenvalue, decay rate |
| θ | theta | Angle |
| μ | mu | Population mean, micro- prefix |
| ω | omega | Angular frequency |
Letters that look like Latin
A few Greek letters are visually identical to Latin ones, so mathematicians avoid them: omicron (Ο/ο) is dropped because it reads as the letter o or a zero, and capital upsilon, zeta, eta, and chi can be mistaken for Y, Z, H, and X. When you copy a letter, prefer the actual Greek glyph rather than a look-alike so search and screen readers treat it correctly.
Typing them elsewhere
In LaTeX, lowercase letters are \alpha, \beta, \gamma and capitals are \Sigma, \Delta, \Omega. In Word, type the name and press Alt (or use Insert → Symbol). Everywhere else, copying from the table above is the fastest route. For operators and relations that sit alongside these letters, see the math symbols reference; lowercase σ in particular shows up in the standard deviation calculator.