Mu
Mu (Μ, μ) is the twelfth letter of the Greek alphabet. μ is the metric prefix micro, one millionth (μg is a microgram); the mean in statistics; the coefficient of friction; and magnetic moment and the muon in physics.
How to read it
Mu is said MYOO in Britain and MOO in America (Cambridge Dictionary: /mjuː/ and /muː/). The University of Arizona’s guide gives its Modern Greek name as Μύ, “mi”, with an m sound.
Also searched as: micro symbol, mu letter, mu symbol, μ, Μ, μ meaning.
Capital, small and look-alike forms
| Form | Character | Code point | Unicode name |
|---|---|---|---|
| Capital | Μ | U+039C | Greek capital letter mu |
| Small | μ | U+03BC | Greek small letter mu |
| Micro sign | µ | U+00B5 | Micro sign |
The capital Μ looks like the Latin M (Cambridge Dictionary gives the symbols M and μ). The micro sign µ is a separate character from the Latin-1 set that looks the same as the small mu; Unicode cross-refers each to the other.
Mu as micro
μ is the SI prefix micro, 10⁻⁶ or one millionth, as in μg for a microgram (NIST, Metric (SI) Prefixes).
Mu in statistics
μ is the mean of a normal distribution. Jeff Miller’s history of mathematical symbols says that use was surprisingly late to settle: R. A. Fisher wrote m from 1912 and switched to μ in the 1936 edition of Statistical Methods for Research Workers.
In AI and machine learning
Google’s Machine Learning Crash Course normalises a feature to its Z-score with x′ = (x − μ)/σ, where μ is the mean and σ the standard deviation. PyTorch’s stochastic gradient descent optimiser uses μ for momentum, which carries part of each step into the next (bₜ = μbₜ₋₁ + …).
In quantum physics
μ is magnetic moment. OpenStax’s University Physics gives the orbital magnetic dipole moment of an electron’s current loop as μ = IA, the current times the loop’s area. The Bohr magneton is written μ_B; NIST’s 2022 CODATA value is 9.274 010 0657 × 10⁻²⁴ joules per tesla. μ is also the muon, a particle over 200 times heavier than the electron but otherwise like it (OpenStax).
Other uses of mu
In mechanics μ is the coefficient of friction: μₛ for static friction and μₖ for kinetic (OpenStax, University Physics). In electromagnetism μ₀ is the vacuum magnetic permeability, 1.256 637 061 27 × 10⁻⁶ N A⁻² in NIST’s 2022 CODATA values.
Write in Greek letters
stringmash.comGreek alphabet translatorWrite English in Greek letters by sound, or turn Greek back into Latin letters as Greek passports do.Read next
- Next in Greek lettersNuNu (Ν, ν) is the 13th letter of the Greek alphabet, said “noo” or “nyoo” and written n in Latin letters. In science the small ν stands for quantities such as a frequency or kinematic viscosity.
- In Statistics symbolsSample mean (x̄)x̄, said “x bar”, is the sample mean: the average of the values in a sample, their total divided by how many there are. The mean of a whole population is written with the Greek letter μ instead.
More greek letters
The same shape elsewhere
Browse symbols drawn with letters and numbers.
Sources
- Greek and Coptic: Range 0370–03FF (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, Greek and Coptic, pp. 39–41
- C1 Controls and Latin-1 Supplement (code chart, Range 0080–00FF), The Unicode Standard, Version 18.0, Unicode Consortium, C1 Controls and Latin-1 Supplement, 00B5
- mu (Cambridge Dictionary entry), Cambridge Advanced Learner’s Dictionary & Thesaurus, Cambridge University Press, mu, noun
- mu (American Heritage Dictionary entry), The American Heritage Dictionary of the English Language, Fifth Edition, HarperCollins Publishers, mu, n.
- Modern Greek Alphabet And Phonetics, University of Arizona, Center for Middle Eastern Studies, Letter table
- Metric (SI) Prefixes, U.S. National Institute of Standards and Technology, SI prefixes table
- Earliest Uses of Symbols in Probability and Statistics, Jeff Miller, Earliest Uses of Various Mathematical Symbols, MacTutor History of Mathematics, University of St Andrews, Moments; the mean of the normal distribution
- Numerical data: Normalization, Machine Learning Crash Course, Google for Developers, Z-score scaling
- torch.optim.SGD, PyTorch 2.14 documentation, PyTorch Foundation, Algorithm
- University Physics Volume 1, 6.2 Friction, OpenStax (Rice University), Equations 6.1 and 6.2
- University Physics Volume 3, 8.2 Orbital Magnetic Dipole Moment of the Electron, OpenStax (Rice University), Equation 8.13
- CODATA Value: Bohr magneton, 2022 CODATA recommended values, U.S. National Institute of Standards and Technology, Value
- CODATA Value: vacuum magnetic permeability, 2022 CODATA recommended values, U.S. National Institute of Standards and Technology, Value
- University Physics Volume 3, 11.1 Introduction to Particle Physics, OpenStax (Rice University), Section 11.1, leptons
Researched, edited and approved by Rory Hansen before publishing. Last reviewed September 30, 2026. How we research
Added .