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, non-italic) is a 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 Greek word {{lang|el|μικρός}} ({{lang|el-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 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. * 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> * 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>[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 fonts, although most fonts use the same 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 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">{{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}} [https://www.bgu.ac.il/~averbukh/ISO_2955-1983E.pdf]</ref>), 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=https://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 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 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'' 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"/>

==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="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>

Category:SI prefixes