Micro-

Template:Short description {{#invoke:other uses|otheruses}} Template:Sister project Template:Use dmy dates Micro (Greek letter μ, mu, non-italic) is a unit prefix in the metric system denoting a factor of one millionth (10⁻⁶).<ref name="Gold">Template:SIbrochure8th</ref> It comes from the Greek word {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning "small".<ref>"MICR," Merriam-Webster.com Dictionary, https://www.merriam-webster.com/dictionary/MICR. Accessed 10/13/2024.</ref>

It is the only SI prefix which uses a character not from the Latin alphabet. In Unicode, the symbol is represented by Template:Unichar or the legacy symbol Template:Unichar.

When Greek characters are not available, the letter "u" is sometimes used instead of "μ". The prefix "mc" is also commonly used; for example, "mcg" denotes a microgram.<ref name="ISMP_2021"/>

Examples

• Typical bacteria are 1 to 10 μm in diameter.
• Human hair typically varies in diameter from 17 to 181 μm.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

• Eukaryotic cells are typically 10 to 100 μm in diameter.<ref>Biology by Campbell & Reece, tenth edition. Ch. 6 "A Tour of the Cell". p. 98.</ref>

Symbol encoding in character sets

The official symbol for the SI prefix micro is a Greek lowercase mu (μ).<ref>Prefixes of the International System of Units, International Bureau of Weights and Measures (page visited on 9 May 2016).</ref> For reasons stemming from its design, Unicode has two different character codes for the letter, with slightly different appearance in some fonts, although most fonts use the same glyph. Template:Unichar (Template:Keypress) is in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1987),<ref>(Unicode 1.0, 1991)</ref> residing at this code point also in DEC MCS (since 1983) and ECMA-94 (since 1985). Template:Unichar (Template:Keypress) is in the Greek range. According to The Unicode Consortium, the Greek letter character is preferred,<ref>Unicode Technical Report #25</ref> 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,<ref name="ISO_2955-1974">Template:Cite book</ref> withdrawn 2001<ref name="ISO_2955-1983">Template:Cite book [1]</ref>), DIN 66030 (since 1980<ref name="DIN_66030_1980">Template:Cite book</ref><ref name="Computerwoche_1981_DIN">Template:Cite journal</ref>) and BS 6430 (since 1983) allow the prefix μ to be substituted by the letter u (or even U, if lowercase letters are not available), as, for example, in um for μm, or uF for μF, or in the common abbreviation UC for microcontroller (μC). Similarly, capacitor values according to the RKM code defined in IEC 60062 (since 1952) can be written as 4u7 (or 4U7) instead of 4μ7 if the Greek letter μ is not available.

The CJK Compatibility block contains square forms of some Japanese katakana measure and currency units. Template:Unichar corresponds to {{#invoke:Lang|lang}} Template:Transliteration.

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.<ref name="Tietz_PT2241">Template:Citation</ref> The two alternatives are to abbreviate as "mcg"<ref name="Tietz_PT2241"/><ref name="ISMP_2021"/> or to write out "microgram" in full (see also List of abbreviations used in medical prescriptions). The alternative abbreviation may be ambiguous in rare circumstances in that mcg could also be read as a micrigram, i.e. 10⁻¹⁴ g; however the prefix micri is not standard, nor widely known, and is considered obsolete. This deprecation, focused on avoiding incorrect dosing in contexts where handwriting is often present, does not extend to all health-care contexts and institutions (for example, some clinical laboratories' reports adhere to it, whereas others do not<ref name="Tietz_PT2241"/>), and in physical sciences research, "μg" remains the sole official abbreviation.

In medical data exchange according to the Health Level 7 (HL7) standard, the μ can be replaced by u as well.<ref name="HL7_2015"/>

See also

• Microgram
• Microscope
• Microsecond
• Microwave
• Square micrometre
• List of commonly used taxonomic affixes