Mu Symbol (μ / µ / Μ): How to Type, Copy, and Use It
The mu symbol has two everyday forms and a twist most guides skip. The lowercase is written μ and the capital is Μ, and there is a near-twin, the micro sign µ, that looks the same on screen but is a different character underneath. Mu is the twelfth letter of the Greek alphabet, though you probably meet it as the sign for “micro,” the coefficient of friction, or the mean of a data set. Here is how to type each one, where to copy them, and which mu you actually want.
In a hurry?
- Copy it: click μ, µ, or Μ in the grid below.
- Windows, for units: hold Alt and type 0181 for µ, the micro sign used in µm, µg, µF.
- Windows, for the Greek letter: in Word, type 03BC then Alt + X for the true μ.
- Mac: press Option + m for µ, or open the Character Viewer and search mu.
- In HTML the letter is
μand the micro sign isµ.
Table of Contents
Two of these look identical but are different characters. Use the micro sign µ for units like µm and µg, and the Greek mu μ for math and physics. The next section shows why that matters.
Mu symbol: every code in one table
The Greek mu, the micro sign, and the capital, side by side with the code for each. The first two look the same but sit at different code points, which is the whole catch with mu.
| Method | μ (Greek mu) | µ (micro sign) | Μ (capital) |
| Unicode | U+03BC | U+00B5 | U+039C |
| Windows Alt code | None* | Alt + 0181 | None (Character Map) |
| Word (code + Alt+X) | 03BC | 00B5 | 039C |
| Mac | Character Viewer | Option + m | Character Viewer |
| HTML named | μ | µ | Μ |
| HTML numeric | μ | µ | Μ |
| URL / percent | %CE%BC | %C2%B5 | %CE%9C |
*There is no direct Alt code for the true Greek μ. Alt + 0181 (or Alt + 230) gives the micro sign µ, which is the right character for units anyway. If you specifically need the Greek letter, type 03BC then Alt + X in Word, or copy it from the grid.
How to type the mu symbol on any device
On Windows
For units, hold Alt and type 0181 on the numeric keypad for µ (the micro sign); Alt + 230 gives the same character. For the true Greek μ, type 03BC in Word and press Alt + X, or open Character Map (search charmap) and copy it. The keypad codes need Num Lock on and will not work from the top-row numbers.
On Mac
Press Option + m and you get µ, the micro sign, straight away — the quickest route for units. For the Greek letter, open the Character Viewer with Control + Command + Space, search mu, and double-click μ, or add the Greek keyboard and use the m key.
On iPhone and Android
The fastest route is copying μ or µ from the box above. To type it regularly, add a Greek keyboard: on iPhone go to Settings, General, Keyboard, Keyboards, Add New Keyboard, Greek; on Android install a Greek layout. Then μ is on the m key.
In Microsoft Word
Type 03BC then Alt + X for the Greek μ, or 00B5 then Alt + X for the micro sign µ. Use 039C for the capital Μ. Alt + X also runs in reverse to reveal a character’s code.
On Linux
Press Ctrl + Shift + U, type 03bc, then Enter for the Greek μ (use 00b5 for the micro sign). On many layouts AltGr + M also types µ directly.
In HTML and CSS
In HTML, the Greek letter is μ or μ, and the micro sign is µ or µ. The capital is Μ or Μ. In a CSS content value, use \03bc for μ or \00b5 for µ. Serve the page as UTF-8 so the character holds.
What does the mu symbol mean?
Mu does more jobs than almost any Greek letter, and the split runs right down the middle: as the micro sign it is a unit prefix, and as the Greek letter it is a variable in math and physics. Here is each meaning in the field that uses it, starting with the one that causes the most confusion.
The micro sign µ vs the Greek mu μ: why there are two
Unicode has two nearly identical characters. The micro sign µ is U+00B5, kept from older Latin-1 encodings specifically for unit prefixes. The Greek small letter mu μ is U+03BC, meant for Greek text and for math and physics variables. Most fonts draw them the same, so you cannot tell by looking. The practical rule: use µ for units like µm and µg, and μ for a variable like the coefficient of friction. Unicode officially prefers the Greek mu but tells software to accept both, which is why the two float around interchangeably and why a search for “µm” can miss a document that used “μm.”
Mu as “micro”: µm, µs, µF, and µg
As an SI prefix, µ means one millionth (10-6). You see it in µm (micrometers, the old “microns”), µs (microseconds), µF (microfarads, all over electronics), and µg (micrograms). This is the single most common reason people reach for the symbol, and the micro sign µ is the correct character for it. In medicine the prefix is often written out as “mcg” instead, for a reason worth its own section below.
Mu in statistics: the population mean
In statistics, μ is the population mean — the true average of an entire population, as opposed to the sample mean, which gets the symbol x-bar. It anchors the normal distribution, written N(μ, σ2), where μ sets the center and sigma the spread. If you are reading a stats formula, the mu is the Greek letter (U+03BC), not the micro sign.
Mu in physics: friction, permeability, and the muon
Physics leans on μ hard. It is the coefficient of friction (μs for static, μk for kinetic), the magnetic permeability of a material (μ, with μ0 for free space), and the symbol for the muon, a heavy relative of the electron written μ–. It also turns up as reduced mass and as the electric dipole moment. All of these are the Greek letter.
Mu in medicine: µg vs mcg, and why it matters
Micrograms are a dosing workhorse, but handwritten µg can be misread as mg — a thousandfold error. Because of that, many hospitals and pharmacy safety bodies tell staff to write mcg instead of µg on prescriptions and labels. Same quantity, safer to read. If you are working in a clinical setting, follow the local standard rather than defaulting to the symbol.
μ vs µ vs u: telling them apart
Three things get swapped for mu: the Greek letter μ (U+03BC), the micro sign µ (U+00B5), and a plain lowercase u that people type when they cannot find either (as in “um” for micrometers or “uF” for microfarads). They read the same to a human but not to a computer, so a filename, password, or database search that mixes them will quietly fail to match. When it has to be exact, copy the specific character you need and check its code point.
Mu in URLs and encoding
The two characters encode differently. In a link, the Greek μ is percent-encoded as %CE%BC, while the micro sign µ is %C2%B5 — a real, visible sign they are not the same character. The capital Μ is %CE%9C. If a mu shows up as μ or µ or a box, the UTF-8 bytes are being read as an older encoding; set the file, database, and page to UTF-8 and it displays correctly.
Copy-paste HTML codes
Every code for the web and for links, in one place. Copy the entity you need.
| Character | Named entity | Numeric entity | URL (percent) code |
| μ (Greek mu) | μ | μ | %CE%BC |
| µ (micro sign) | µ | µ | %C2%B5 |
| Μ (capital) | Μ | Μ | %CE%9C |
In a CSS content value, use \03bc for the Greek mu or \00b5 for the micro sign. For the sibling alpha, beta, and lambda symbols and every other character, see the copy and paste symbols tool.
Troubleshooting
My mu shows as μ or a box
That is an encoding mismatch — the UTF-8 bytes for the character are being read as an older encoding. Set the file, database, and page charset to UTF-8 and the mu displays correctly.
Alt + 0181 gives µ but my formula needs μ
Those are two characters. Alt + 0181 produces the micro sign (U+00B5), which is right for units but not the Greek variable. For the Greek μ (U+03BC), type 03BC then Alt + X in Word, use the Character Viewer on a Mac, or copy it from the grid above.
My capital mu looks like a normal M
It is supposed to. The capital Μ (U+039C) is drawn the same as the Latin M. If it needs to be unmistakable, use the lowercase μ or label it in words.
Frequently asked questions
How do I type the mu symbol μ?
For units, hold Alt and type 0181 (Windows) or press Option + m (Mac) for the micro sign µ. For the Greek letter μ, type 03BC then Alt + X in Word, or copy it from the grid above.
What does the mu symbol mean?
It depends. As the micro sign it means one millionth, used in units like µm and µg. As the Greek letter it is a variable: the population mean in statistics, and the coefficient of friction, permeability, or the muon in physics.
What is the difference between µ and μ?
They look the same but are different characters. The micro sign µ is U+00B5, meant for unit prefixes; the Greek mu μ is U+03BC, meant for Greek text and math or physics variables. Unicode prefers the Greek letter but accepts both.
How do I type the micro symbol for µm or µF?
On Windows, Alt + 0181. On a Mac, Option + m. In HTML, µ. All of these give the micro sign U+00B5, which is the correct character for units.
How do I write μ in HTML?
Use μ or μ for the Greek letter, and µ or µ for the micro sign. The capital is Μ or Μ. In a URL, μ is %CE%BC and µ is %C2%B5.
