View source for Micro-

{{Short description|Metric system unit prefix, one millionth}}
{{Other uses|Micro (disambiguation){{!}}Micro}}
{{use dmy dates|date=December 2022|cs1-dates=y}}
{{infobox symbol
|mark= μ
|unicode={{unichar|03BC}}
|different from={{unichar|00B5}} (discouraged)
}}
{{Wiktionary|micro-}}
'''''Micro''''' ([[Greek letter]] '''μ''', [[Mu (letter)|mu]], non-[[Italic type|italic]]) is a [[metric prefix|unit prefix]] in the [[metric system]] denoting a factor of one [[millionth]] (10<sup>−6</sup>).<ref name="Gold">{{SIbrochure8th}}</ref> It comes from the [[Ancient Greek|Greek]] word {{lang|grc|μικρός}} ({{lang|grc-Latn|mikrós}}), meaning "small".<ref>"MICR," Merriam-Webster.com Dictionary, https://www.merriam-webster.com/dictionary/MICR. Accessed 10/13/2024.</ref>

It is the only [[International System of Units|SI]] prefix which uses a character not from the [[Latin alphabet]]. In [[Unicode]], the symbol is represented by {{unichar|03BC}} or the legacy symbol {{unichar|00B5}}. The prefix "mc" is also commonly used; for example, "mcg" denotes a [[microgram]] (whereas mg denotes a [[milligram]]).<ref name="ISMP_2021"/>

==Examples==
* Typical [[bacteria]] are 1 to 10 μm in diameter. 
* [[Hair's breadth|Human hair]] typically varies in diameter from 17 to 181 μm.<ref>{{cite web|url=https://hypertextbook.com/facts/1999/BrianLey.shtml|title=Diameter of a human hair|first=Brian|last=Ley|year=1999|website=The Physics Factbook|editor-last=Elert|editor-first=Glenn|accessdate=2018-12-08}}</ref>
* [[Eukaryote|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 [[metric prefix|SI prefix]] ''micro'' is a [[mu (letter)|Greek lowercase mu]] (μ).<ref>[https://www.bipm.org/en/measurement-units/si-prefixes 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 [[computer font]]s, although most fonts use the same [[glyph#Typography|glyph]]. {{unichar|03BC|GREEK SMALL LETTER MU}}  is in the Greek range. According to [[The Unicode Consortium]], the Greek letter character is preferred,<ref>[https://www.unicode.org/reports/tr25 Unicode Technical Report #25]</ref> but implementations must recognize the micro sign as well, for [[Unicode compatibility characters|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, [[International Standards Organization|ISO]] 2955 (since 1974,<ref name="ISO_2955-1974">{{cite book |title=ISO 2955-1974: Information processing - Representations of SI and other units for use in systems with limited character sets |edition=1st |date=1974}}</ref> withdrawn 2001<ref name="ISO_2955-1983">{{cite book |url=http://isotc.iso.org/livelink/livelink/4289384/ISO_2955-1983E_repr_of_SI_units_with_limited_char_sets.pdf?func=doc.Fetch&nodeid=4289384 |title=ISO 2955-1983: lnformation processing - Representations of SI and other units for use in systems with limited character sets |date=1983-05-15 |edition=2nd |chapter=Table 2 |access-date=2016-12-14}} [http://www.bgu.ac.il/~averbukh/ISO_2955-1983E.pdf]</ref>), [[Deutsches Institut für Normung|DIN]] 66030 (since 1980<ref name="DIN_66030_1980">{{cite book |title=DIN 66030: Darstellungen von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat |language=de |edition=1st |date=1980}}</ref><ref name="Computerwoche_1981_DIN">{{cite journal |title=Neue Normen für die Informationsverarbeitung |language=de |journal=[[Computerwoche]] |date=1981-01-09 |url=http://www.computerwoche.de/a/neue-normen-fuer-die-informationsverarbeitung,1184901 |access-date=2016-12-14 |url-status=live |archive-url=https://web.archive.org/web/20161214025700/http://www.computerwoche.de/a/neue-normen-fuer-die-informationsverarbeitung%2C1184901 |archive-date=2016-12-14}}</ref>) and [[British Standards Institution|BS]] 6430 (since 1983) allow the prefix <code>μ</code> to be substituted by the letter {{angbr|u}} ({{unichar2|u}}) as, for example, in <code>um</code> for <code>μm</code>, or <code>uF</code> for <code>μF</code>
.
Similarly, capacitor values according to the [[RKM code]] defined in [[International Electrotechnical Commission|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.
{{Unichar|3343}} corresponds to {{lang|ja|マイクロ}} {{Transliteration|ja|maikuro}}.

==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">{{Citation |last1=Burtis |first1=Carl A. |last2=Ashwood |first2=Edward R. |last3=Bruns |first3=David E. |year=2012 |title=Tietz Textbook of Clinical Chemistry and Molecular Diagnostics |publisher=Elsevier Health Sciences |isbn=978-1455759422 |edition=5th |url=https://books.google.com/books?id=BBLRUI4aHhkC&pg=PT2241 |postscript=.}}</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<sup>−14</sup> g; however the prefix ''[[micri-|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]]

==References==
<references>
<ref name="HL7_2015">{{cite web |title=Commonly Used UCUM Codes for Healthcare Units |date=2015-11-21 |publisher=HL7 Deutschland e.V. |url=https://download.hl7.de/documents/ucum/ucumdata.html |access-date=2022-12-24 |url-status=live |archive-url=https://web.archive.org/web/20221006180404/https://download.hl7.de/documents/ucum/ucumdata.html |archive-date=2022-10-06}}</ref>
<!-- <ref name="HL7_2022">{{cite web |title=Commonly Used UCUM Codes for Healthcare Units |date=2015-11-21 |publisher=HL7 Deutschland e.V. |url=https://howtotypesymbols.com/how-to-type-mu-micro-symbol-in-word-and-mac/ |access-date=2023-01-14 |url-status=live |archive-url=https://web.archive.org/web/20221006180404/https://download.hl7.de/documents/ucum/ucumdata.html |archive-date=2022-10-06}}</ref> -->
<ref name="ISMP_2021">{{cite web |title=ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations: Abbreviations for Doses/Measurement Units |date=2021-02-05 |work=Recommendations |publisher=[[Institute for Safe Medication Practices]] (ISMP) |url=https://www.ismp.org/recommendations/error-prone-abbreviations-list |access-date=2022-12-24 |url-status=live |archive-url=https://web.archive.org/web/20221224213621/https://www.ismp.org/recommendations/error-prone-abbreviations-list |archive-date=2022-12-24 |quote=Error-Prone Abbreviations, Symbols, and Dose Designations: μg […] Intended Meaning: Microgram […] Misinterpretation: Mistaken as mg […] Best Practice: Use mcg […]}}</ref>
</references>

{{SI prefixes (infobox)}}

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[[Category:SI prefixes]]