Mu (μ) in HTML
Mu is the twelfth Greek letter, written Μ and μ. The capital is at U+039C and the small letter at U+03BC, which is a different code point from the micro sign.
At a glance
- Character
- Μ μ
- Named entity
- Μ μ
- Decimal reference
- Μ μ
- Hex reference
- Μ μ
- Unicode code point
- U+039C, U+03BC
- Unicode name
- GREEK CAPITAL LETTER MU, GREEK SMALL LETTER MU
- In the entity reference
- Greek
In detail
Mu is the only Greek letter with a duplicate elsewhere in Unicode. The micro sign at U+00B5 exists purely because it was present in Latin-1 and had to survive the conversion, and it draws the same shape. Compatibility normalisation folds the micro sign onto this letter, so the two are equal after normalising and unequal before, which is a difference that never shows on screen.
In statistics the small mu is the population mean, deliberately distinguished from the sample mean written with a bar over an x. That distinction is the whole point of the notation: one is the true value you are trying to estimate, the other is what your sample gave you, and conflating them in a write up hides the inferential step.
In mechanics it is the coefficient of friction, a dimensionless ratio between the friction force and the normal force, with separate static and kinetic values for the same pair of surfaces. In particle physics the muon takes its name from the letter, and in absorption and viscosity contexts mu turns up again with yet another definition.
For unit prefixes, prefer this letter over the micro sign if you are choosing fresh, since the micro sign is a compatibility character. The important thing is not which one you pick but that you pick one and normalise everything on the way into storage, because a units column containing both is a column that cannot be grouped.
Examples
<p>H₀: μ = 0. The sample gave x̄ = 1.8.</p>₀ is a subscript zero and ̄ a combining macron, which draws the bar over the x.
const micro = "\u00B5m"; // micro sign
const greek = "\u03BCm"; // Greek small letter mu
micro === greek; // false
micro.normalize("NFKC") === greek.normalize("NFKC"); // trueThings that catch people out
- Two code points draw the same glyph. Any unit stored as free text will eventually contain both, and no visual review will find it.
- The population mean and the sample mean are different quantities. Using mu for a sample average overstates what the number is.
- Coefficients of friction come in static and kinetic pairs. Quoting one value for a surface pair without saying which is incomplete.
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Related HTML entities
All html entities →Micro sign (µ) in HTML
The micro sign at U+00B5 and the Greek small mu at U+03BC look identical and are different code points. Which one to use for units, and how to normalise them.
Sigma (σ) in HTML
The Greek letter sigma at U+03A3 and U+03C3, its entity forms, the summation operator it is confused with, and the final sigma used at the end of a word.
Lambda (λ) in HTML
The Greek letter lambda at U+039B and U+03BB, its entity forms, its use for wavelength and decay, and where the anonymous function name came from.
Pi (π) in HTML
The Greek letter pi at U+03A0 and U+03C0, its entity forms, the capital pi that is not the product operator, and how to write pi in code correctly.
Phi (φ) in HTML
The Greek letter phi at U+03A6 and U+03C6, its entity forms, the loopy and straight glyph variants, and the golden ratio it conventionally names.
Omega (ω) in HTML
The Greek letter omega at U+03A9 and U+03C9, its entity forms, the separate ohm sign that normalises onto it, and its use for angular frequency.
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