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Mu

The mu symbol μ is the Greek letter, and the micro sign µ is a separate character that looks the same. Tap to copy, then see the codes, how to type each one, and what mu means for micro, mean, friction and viscosity.

By Maya Chen, lettering designer and type educator · Checked by Jordan Hale · · How we review content

Copy mu

One tap copies one character. Each form below has its own code point.

Key facts

  • Mu is the 12th letter of the Greek alphabet, with a numeral value of 40; Greek small mu is U+03BC.
  • The micro sign µ (U+00B5) is a separate character that normalises under NFKC to Greek mu μ (U+03BC).
  • As an SI prefix, μ means micro, one millionth (10⁻⁶), as in μm for micrometre and μs for microsecond.
  • In statistics, μ is the population mean, and a normal distribution is written N(μ, σ²).
  • LaTeX has no \Mu command, so capital mu is typed as a plain M.

Codes for every form

Unicode names and code points for each form, with the escapes you need in HTML, CSS, JavaScript and LaTeX.

Mu: Unicode name, code point, decimal value, HTML entities, CSS and JavaScript escapes, and LaTeX command for each form
FormUnicode nameCode pointDecimalHTMLCSS / JavaScriptLaTeX
mu, lowercaseGREEK SMALL LETTER MUU+03BC956μ μ\03BC / \u03BC\mu
mu, capitalGREEK CAPITAL LETTER MUU+039C924Μ Μ\039C / \u039Cnone

LaTeX has no command for capital mu. Type a plain M.

How to type mu

The quick methods for this letter. Step-by-step instructions for each system, and what we have and have not tested, are on how to type Greek letters.

Ways to type mu
MethodWhat to do
Copy and pasteUse the buttons at the top of this page. Pasted text is plain Unicode.
Word on WindowsType the code, then press Alt+X: 03BC for μ; 039C for Μ. Windows steps.
Excel and Google Sheets=UNICHAR(956) for μ; =UNICHAR(924) for Μ. Office steps.
PhoneAdd a Greek keyboard: iPhone and iPad or Android.
Web page or LaTeXμ, \mu for μ; Μ for Μ. LaTeX commands work in math mode.

Characters that look like mu

These are separate characters, so each has its own code point. Copy the one that matches the job.

How to say mu

Mu pronunciation in English, modern Greek and classical Greek
ReadingValue
English (maths and science)MYOO, /mjuː/
Modern Greek/m/. The modern Greek name is μι, pronounced /mi/.
Classical Greek (reconstructed)/m/. The classical name μῦ was pronounced /mŷː/.

English speakers say "mew" for the symbol, as in micro. The letter represents a /m/ sound in every period of Greek. The name changed: ancient μῦ sounded like "moo" with a long vowel, and modern Greek says "mee", per Wikipedia. See the pronunciation page for the whole alphabet.

What mu means, field by field

"Standard" marks a definition or notation that is fixed, such as an SI unit or a named function. "Convention" marks common practice that varies by author, so check the definitions in your own text. The same letter often means different things in different fields; the full table for every letter is on Greek letters in math and science.

  • Unitssymbol μ, µStandard

    The SI prefix micro, one millionth (10⁻⁶), as in μm for micrometre, μg for microgram and μs for microsecond. The prefix is written as a Greek letter or the micro sign, both of which look the same.

  • Statisticssymbol μConvention

    The population mean. A normal distribution is written N(μ, σ²), with mean μ and variance σ². The sample mean is x̄ instead.

  • Mechanicssymbol μConvention

    The coefficient of friction, the ratio of the friction force to the normal force. It carries a subscript for the case, μₛ for static and μₖ for kinetic friction.

  • Electromagnetismsymbol μ, μ₀Standard

    Magnetic permeability. μ₀ is the vacuum value, called the magnetic constant. It links magnetic field strength to flux density.

  • Fluid mechanicssymbol μConvention

    Dynamic viscosity, in pascal-seconds. Some texts use η for the same quantity, and kinematic viscosity is ν.

  • Mechanicssymbol μStandard

    Reduced mass of a two-body system, μ = m₁m₂/(m₁ + m₂). Used to turn a two-body problem into a one-body one.

  • Chemistrysymbol μConvention

    Chemical potential and electric dipole moment both use μ. The context and the units show which one is meant.

  • Particle physicssymbol μStandard

    The muon, a heavier cousin of the electron. It is written μ⁻ or μ⁺, according to charge.

  • Number theorysymbol μ(n)Standard

    The Möbius function: μ(1) = 1, μ(2) = −1, μ(4) = 0 and μ(6) = 1. It is a function name, not a mean.

Lookalikes and common mistakes

  • μ and µ are two different characters

    Greek small letter mu is U+03BC. The micro sign µ is U+00B5 and comes from the Latin-1 character set. They look alike, and NFKC normalisation turns the micro sign into the Greek letter. If text will be searched or compared, use μ; if a tool gives you µ, it will not match μ until it is normalised.

  • Your keyboard may type the micro sign

    On a US Mac layout, Option+M types µ (MICRO SIGN) and on Windows Alt+230 gives µ through code page 437. Both are lookalikes. Copy the Greek μ from the button above if you need the letter. We have not tested these on live systems.

  • Plain u and "ug" are risky fallbacks

    Plain u is a common fallback for μ, as in "ug" for μg, but it is ambiguous and easy to misread. Medical safety lists flag μg as a character that gets mistaken for mg and ask for "mcg" instead, so follow your institution's list. A μm misread as mm is a thousandfold error, so keep the symbol clear or spell the unit out.

  • Lowercase μ is not u, and Μ is not M

    In small type, μ resembles a u with a tail on the left. Capital Μ is identical to Latin M and Cyrillic М in most fonts, and three different code points are in circulation. If you need the Greek letter, copy it.

  • Square compatibility characters are not the units

    ㎛ ㎍ ㎲ and ㎕ are single characters for μm, μg, μs and μL, made for East Asian typesetting. They look cramped next to ordinary text, and screen readers handle them inconsistently. Write the two letters instead.

Where does the mu symbol come from?

Mu is the 12th letter of the Greek alphabet, with a numeral value of 40. It descends from the Phoenician letter mem, which started as a hieroglyph for water, and the Latin M and Cyrillic М descend from it, according to Wikipedia. The ancient name μῦ became μι in modern Greek, though both stand for the sound /m/.

Why are there two mus in one document?

Mu is the letter that most often arrives in text as the wrong character. The reason is history: the Latin-1 character set (ISO 8859-1) included a MICRO SIGN at U+00B5 as part of its Western European repertoire, and Unicode kept it for compatibility while giving the Greek letter its own code point at U+03BC. Under compatibility normalisation, µ folds to μ. The square unit characters such as ㎛ and ㎍ fold to μ followed by plain letters, which shows which one Unicode regards as the real thing.

For documents you write now, use the Greek letter for the micro prefix. It is the code point that normalisation settles on, so text normalised with NFKC ends up with it whichever character it started as. The two look the same on screen, so the difference matters mostly when text is searched, sorted or parsed.

How do you tell μ the statistic from μ the prefix?

The two most common uses never meet in one formula, but they do meet in one document. In a lab report, μ before a unit is a prefix (5 μm) while μ alone with an equals sign is the mean (μ = 12.4). The giveaway is whether a unit letter follows directly. If it does, it is a prefix; if not, check the definitions.

How do you write μ in code and markup?

In HTML, μ and Μ are named entities, μ is the numeric form, and µ is the named entity for the micro sign µ. In CSS, the escape for the Greek letter is \03BC. In LaTeX math, \mu gives the letter, and there is no \Mu: type a plain M. In running text, the textgreek package has \textmu, and siunitx handles units with \micro.

Sources

These sources back the facts on this mu symbol page. What mu stands for depends on the field; follow the definition in your own source.

Frequently asked questions

Basics

What does mu mean in statistics?
Lowercase μ is the population mean, the average of every value in the group you are describing. The sample mean is written x̄ instead. Together with σ, the standard deviation, μ defines a normal distribution, written N(μ, σ²), so a statistics text will usually define both near the first formula.
Where does the mu symbol come from?
Mu is the 12th letter of the Greek alphabet, with a numeral value of 40. It descends from the Phoenician letter mem, which started as a hieroglyph for water, and the Latin M and Cyrillic М descend from it, according to Wikipedia. The ancient name μῦ became μι in modern Greek, though both stand for /m/.

Where it works

What does mu mean in physics?
It depends on the topic. μ is the coefficient of friction in mechanics, the magnetic permeability in electromagnetism, the dynamic viscosity in fluid mechanics and the reduced mass of a two-body system. As a prefix, it means micro, one millionth. The units and subscripts tell you which meaning is in play.
What do μ and μ₀ mean in electromagnetism?
In electromagnetism, μ is magnetic permeability, and μ₀ is its vacuum value, called the magnetic constant. It links magnetic field strength to flux density. The subscript zero is what separates the vacuum constant from the permeability of a material, so a bare μ next to a unit letter is more likely the micro prefix.
What is μ(n) in the Möbius function?
μ(n) is the Möbius function from number theory, so μ(1) = 1, μ(2) = −1, μ(4) = 0 and μ(6) = 1. Here μ is a function name, not a mean or a prefix. The brackets after the letter and the integer inside them are the giveaway, so no unit or distribution is involved.

How it works

How do I type the mu symbol?
Copy μ from this page, or type 03BC in Word and press Alt+X. In Excel or Google Sheets, =UNICHAR(956) returns the Greek μ and =UNICHAR(181) returns the micro sign µ. On a US Mac layout, Option+M gives µ, and on Windows Alt+230 gives µ. The how-to page covers phones, and marks the steps we have not tested.
How do I write micrometre or microlitre in plain text?
Write μm or µm for micrometre and μL or µL for microlitre, with a space between the number and the unit, as in 5 μm. Use the Greek letter where you can. If the text must be pure ASCII, "um" is a common fallback in print, but it is ambiguous, so spell the unit out first.
How do I write the mu symbol in HTML and LaTeX?
In HTML, μ and Μ are the Greek letters, μ is the numeric form, and µ is the micro sign µ. In LaTeX math, \mu gives the letter and there is no \Mu, so type a plain M. In running text, the textgreek package has \textmu, and siunitx handles units with \micro.

Tips & limits

Is the mu symbol the same as the micro sign?
No. μ is GREEK SMALL LETTER MU (U+03BC) and µ is MICRO SIGN (U+00B5). They look the same and both are used for the micro prefix. Compatibility normalisation (NFKC) turns the micro sign into the Greek letter, so the letter is the safer choice for text that will be searched. For plain display the two are interchangeable.
Is the mu in friction the same as the mu in viscosity?
It is the same letter standing for different quantities. In mechanics, μ is the coefficient of friction, with μₛ for static and μₖ for kinetic friction. In fluid mechanics, μ is dynamic viscosity in pascal-seconds, though some texts use η for it. The field, units and subscripts tell you which one is meant.

Related Greek pages and symbols