Greek alphabet
Letters, names, pronunciation and what each one usually means in science.
Alpha
AL-fuh
Angles, significance level, thermal expansion, alpha particles
Beta
BAY-tuh
Angles, regression coefficients, type II error, beta decay
Gamma
GAM-uh
Gamma function, Lorentz factor, surface tension, gamma rays
Delta
DEL-tuh
Change or difference (Δ), infinitesimals (δ), the Laplacian
Epsilon
EP-si-lon
A very small quantity, permittivity, strain, error terms
Zeta
ZAY-tuh
The Riemann zeta function, damping ratio
Eta
AY-tuh
Efficiency, viscosity, learning rate
Theta
THAY-tuh
Angles above all else; also temperature and asymptotic bounds
Iota
eye-OH-tuh
Rare — it looks too much like i and 1
Kappa
KAP-uh
Curvature, thermal conductivity, dielectric constant
Lambda
LAM-duh
Wavelength, eigenvalues, decay constant, Poisson rate, lambda calculus
Mu
MEW
Population mean, coefficient of friction, the SI prefix micro
Nu
NEW
Frequency, kinematic viscosity, degrees of freedom
Xi
ZY or KSEE
Random variables, correlation length
Omicron
OM-i-kron
Almost never — it is identical to the letter o
Pi
PIE
The circle constant (π), product notation (Π), osmotic pressure
Rho
ROW
Density, resistivity, correlation coefficient
Sigma
SIG-muh
Summation (Σ), standard deviation (σ), stress, conductivity
Tau
TAW or TOW
Torque, time constant, shear stress, 2π
Upsilon
UP-si-lon
Rare in mathematics; a particle in physics
Phi
FIE or FEE
The golden ratio, angles, magnetic flux, Euler’s totient, the normal CDF
Chi
KY
The chi-squared distribution, electronegativity, susceptibility
Psi
SIGH or PSY
Wavefunctions in quantum mechanics, stream function
Omega
oh-MAY-guh
Ohms (Ω), angular velocity (ω), the sample space
How it works
Mathematics and the sciences borrowed the Greek alphabet for the simple reason that the Latin one ran out. Over centuries, individual letters accumulated strong conventional meanings — seeing σ in a statistics paper tells you it is a standard deviation before you read a word.
Case carries meaning
Upper and lower case are usually different quantities entirely. Σ is summation while σ is standard deviation; Δ is a change while δ is an infinitesimal; Π is a product while π is the circle constant. Getting the case wrong changes the statement.
The letters nobody uses
Omicron and iota are almost absent from mathematical notation because they are visually identical to o and i. Capital Alpha, Beta, Epsilon, Zeta, Eta, Iota, Kappa, Mu, Nu, Omicron, Rho, Tau, Upsilon and Chi are all identical to Latin capitals, so they are rarely used either.
Typing them
Copy from this page, or in LaTeX write \alpha, \Sigma and so on. On
Windows, Alt codes work; on macOS, the Greek keyboard layout or the character viewer. In
HTML, named entities such as α and π are available.