The micro sign (µ) used for microns, micrograms, and microseconds — and why it's a completely different character from the identical-looking Greek letter mu. Click any symbol to copy it instantly.
The micro sign (µ, U+00B5) and the Greek small letter mu (μ, U+03BC) render as the exact same glyph in almost every font, but Unicode treats them as two separate characters. Which one you paste can quietly break search, regex matching, and filenames without ever looking wrong on screen.
The legacy micro sign, retained in Unicode for compatibility with older Latin-1 (ISO/IEC 8859-1) systems. Used for µm (micron), µg (microgram), µs (microsecond).
The actual twelfth letter of the Greek alphabet — visually identical to the micro sign and the character Unicode's own normalization rules prefer.
The micro sign (µ, U+00B5) exists in Unicode purely for backward compatibility. It was inherited from ISO/IEC 8859-1 (Latin-1), the 8-bit encoding that predates Unicode and is still baked into countless legacy systems, fonts, and file formats. The Unicode Consortium's own guidance is that the Greek small letter mu (μ, U+03BC) is the preferred character for the SI "micro" prefix — µg, µm, µs — but software must keep recognizing U+00B5 too, because so much existing text already uses it.
The two characters are visually identical in nearly every font, and Unicode's own NFKC normalization rule folds the micro sign down to Greek mu automatically. That's usually invisible — until it isn't: a search, a regex match, a filename comparison, or a database lookup can silently fail when one string uses U+00B5 and the other uses U+03BC, because to a byte-level comparison they're different characters even though no human can tell them apart on screen. It's a common enough gotcha that developers file real bug reports over it — a 2025 Home Assistant pull request, for example, proposed switching the project's unit strings from the micro sign to Greek mu specifically to avoid this class of mismatch.
| Platform / Tool | Method |
|---|---|
| Windows (legacy NumPad Alt code) | Alt+0181 — micro sign (Windows-1252 position) |
| Mac | Option+M — micro sign |
| Word / Windows (Unicode input) | Type 00B5 (micro) or 03BC (mu), then Alt+X |
| HTML | µ or µ (micro sign); μ or μ (Greek mu) |
CSS content | content: "\B5" (micro) or content: "\3BC" (mu) |
| LaTeX | \textmu (textcomp package) for the micro sign; $\mu$ for Greek mu |
No — they're visually identical but Unicode gives them different code points (U+00B5 for the micro sign, U+03BC for Greek mu), and the difference can silently break search, regex matching, and string comparisons even though nothing looks wrong on screen.
Either renders correctly for a human reader, but the Unicode Consortium recommends Greek mu (μ, U+03BC) for new text, since NFKC normalization already converts the micro sign to it automatically. Use the micro sign only when matching an existing legacy system that specifically expects it.
Because they're different Unicode characters. A plain-text search usually does an exact byte match and won't treat U+00B5 and U+03BC as equivalent unless the search explicitly normalizes text first (NFKC).
No — in virtually every font they render as the same glyph. The difference is entirely at the character-encoding level, invisible until code, search, or file-matching tools are involved.
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