Micro (Greek letter μ, mu, non-italic) is a unit prefix in the metric system denoting a factor of one millionth (10<sup>−6</sup>). It comes from the Greek word (), meaning "small".
It is the only SI prefix which uses a character not from the Latin alphabet. In Unicode, the symbol is represented by or the legacy symbol . The prefix "mc" is also commonly used; for example, "mcg" denotes a microgram (whereas mg denotes a milligram).
- Eukaryotic cells are typically 10 to 100 μm in diameter.
Symbol encoding in character sets
The official symbol for the SI prefix micro is a Greek lowercase mu (μ). For reasons stemming from its design, Unicode has two different character codes for the letter, with slightly different appearance in some computer fonts, although most fonts use the same glyph. is in the Greek range. According to The Unicode Consortium, the Greek letter character is preferred, but implementations must recognize the micro sign as well, for compatibility with legacy character sets. This distinction also occurs in some legacy code pages, notably Windows-1253.
In circumstances in which only the Latin alphabet is available, ISO 2955 (since 1974, withdrawn 2001), DIN 66030 (since 1980) and BS 6430 (since 1983) allow the prefix <code>μ</code> to be substituted by the letter () as, for example, in <code>um</code> for <code>μm</code>, or <code>uF</code> for <code>μF</code>
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Similarly, capacitor values according to the RKM code defined in IEC 60062 (since 1952) can be written as <code>4u7</code> (or <code>4U7</code>) instead of <code>4μ7</code> if the Greek letter <code>μ</code> is not available.
The CJK Compatibility block contains square forms of some Japanese katakana measure and currency units.
corresponds to .
Other abbreviating conventions
In some health care institutions, house rules deprecate the standard symbol for microgram, "μg", in prescribing or chart recording, because of the risk of giving an incorrect dose because of the misreading of poor handwriting. The two alternatives are to abbreviate as "mcg"
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