Greek Alphabet in Engineering

The 24 Greek letters with upper and lower case and the symbols they usually stand for in engineering.

Engineers run out of Latin letters quickly, so Greek letters stand for many quantities: α for angular acceleration, σ for stress, ρ for density, ω for angular velocity, Ω for ohms. This chart lists all 24 letters with their upper and lower case forms and the meanings they commonly carry in mechanics, heat transfer, electrical engineering and statistics.

The table

24 rows

Name	Upper case	Lower case	Position in the alphabet	Common uses in engineering
Alpha	Α	α	1	angular acceleration, thermal diffusivity, coefficient of thermal expansion
Beta	Β	β	2	angle, current gain of a transistor, reliability index
Gamma	Γ	γ	3	shear strain, heat capacity ratio, specific weight
Delta	Δ	δ	4	a change or difference (upper case), deflection, small change
Epsilon	Ε	ε	5	strain, permittivity, emissivity, small error
Zeta	Ζ	ζ	6	damping ratio
Eta	Η	η	7	efficiency, dynamic viscosity (sometimes)
Theta	Θ	θ	8	angle, temperature, angular position
Iota	Ι	ι	9	rarely used in engineering
Kappa	Κ	κ	10	curvature, thermal conductivity (older texts)
Lambda	Λ	λ	11	wavelength, eigenvalue, thermal conductivity, failure rate
Mu	Μ	μ	12	micro (10 to the minus 6), coefficient of friction, dynamic viscosity, mean
Nu	Ν	ν	13	kinematic viscosity, Poisson ratio, frequency
Xi	Ξ	ξ	14	damping or a generalized coordinate
Omicron	Ο	ο	15	rarely used
Pi	Π	π	16	ratio of circumference to diameter (lower case), product (upper case)
Rho	Ρ	ρ	17	density, resistivity, correlation coefficient
Sigma	Σ	σ	18	normal stress, standard deviation, sum (upper case), electrical conductivity
Tau	Τ	τ	19	shear stress, time constant, torque
Upsilon	Υ	υ	20	rarely used
Phi	Φ	φ	21	angle, phase, magnetic flux, diameter symbol (similar)
Chi	Χ	χ	22	chi-squared statistic
Psi	Ψ	ψ	23	angle, stream function, pressure (psi unit is unrelated)
Omega	Ω	ω	24	angular velocity (lower case), ohm (upper case), solid angle

Source and notes: The 24 letters of the modern Greek alphabet. Uses are the common conventions in mechanics, heat transfer, electrical engineering and statistics; meanings differ between fields and authors, so always define a symbol where you first use it.

How to use this table

Find the letter by its name or shape (the filter box searches the uses too).
Check the meaning in your field: the same letter means different things in different subjects.
Always define a symbol where you first use it.

Worked example: reading a formula

In the Reynolds number Re = ρ v D ÷ μ, ρ (rho) is the density and μ (mu) the dynamic viscosity; with kinematic viscosity ν (nu) it becomes Re = v D ÷ ν.
In σ = F ÷ A σ (sigma) is normal stress; in τ = T r ÷ J τ (tau) is shear stress; and in η = P_out ÷ P_in η (eta) is efficiency.

Notes and cautions

Upper-case letters that look like Latin ones (Α, Β, Ε, Ζ, Η, Ι, Κ, Μ, Ν, Ο, Ρ, Τ, Υ, Χ) are rarely used as symbols: lower case is far more common.
The symbol φ (phi) is often confused with the diameter symbol ⌀ and with the empty-set sign ∅; they are different characters.
μ for micro (10⁻⁶) is the Greek letter mu; in plain text it is often written “u”.

FAQ

What is the symbol for ohms?

The upper-case omega, Ω.

What does sigma stand for?

Normal stress, a standard deviation (lower case σ) or a sum (upper case Σ).

What is pi?

The ratio of a circle’s circumference to its diameter, 3.14159265… (lower case π).

Sources

The Unicode Standard, Greek and Coptic block; ISO 80000-1 (quantities and units: general) for the symbols of quantities.
The 24 letters of the modern Greek alphabet. Uses are the common conventions in mechanics, heat transfer, electrical engineering and statistics; meanings differ between fields and authors, so always define a symbol where you first use it.