{{short description|Unit of mass}} {{hatnote|"μg" and "ΜG" (Greek letter mu with G) redirect here. For microgravity, see micro-g environment. Not to be confused with MG (in Latin letters) or uG (in Latin letters).}} {{infobox unit | name = microgram | image = Radiance multivitamins nutritional information crop.jpg | caption = A nutrition facts label displaying, for example, the amount of folic acid in micrograms | standard = SI | quantity = mass | symbol = μg }} In the metric system, a '''microgram''' or '''microgramme''' is a unit of mass equal to one millionth ({{val|e=-6}}) of a gram. Two different abbreviations are commonly used. The International System of Units (SI) uses '''μg''', where the SI prefix "micro-" is represented by the Greek letter μ (mu). The abbreviation '''mcg''' is preferred for medical information in the United States (US), but prescription writing guidance in the United Kingdom advises that "microgram" should not be abbreviated.<ref>{{cite web |title=Prescription writing |url=https://bnf.nice.org.uk/medicines-guidance/prescription-writing/ |website=BNF |publisher=National Institute for Health and Care Excellence |access-date=9 November 2025}}</ref> A third abbreviation, the Greek letter '''γ''' (gamma), is no longer recommended.<ref>[https://www.nist.gov/pml/weights-and-measures/publications/nist-handbooks/handbook-133 NIST Handbook 133 – 2018] {{Webarchive|url=https://web.archive.org/web/20180804140757/https://www.nist.gov/pml/weights-and-measures/publications/nist-handbooks/handbook-133 |date=2018-08-04 }}, [https://www.nist.gov/sites/default/files/documents/2017/04/28/12-apde-gentab-11-hb133-final.pdf#page=17 Appendix E. General Tables of Units of Measurement, page 159 (17)] {{Webarchive|url=https://web.archive.org/web/20170505220914/https://www.nist.gov/sites/default/files/documents/2017/04/28/12-apde-gentab-11-hb133-final.pdf#page=17 |date=2017-05-05 }}</ref> The US Institute for Safe Medication Practices (ISMP) and the US Food and Drug Administration (FDA) recommend that mcg should be used, rather than μg, when communicating medical information.<ref>{{cite web |title=ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations |url=https://www.ismp.org/recommendations/error-prone-abbreviations-list |access-date=2018-03-28 |publisher=ISMP |archive-date=2018-01-27 |archive-url=https://web.archive.org/web/20180127224608/http://www.ismp.org/tools/errorproneabbreviations.pdf |url-status=live }}</ref> This is due to the risk that μ might be misread as m, for "milli-", which is equal to one thousandth ({{val|e=-3}}). Such a misreading could result in a thousandfold overdose of a drug or medicine. However, mcg is also the symbol for the obsolete unit millicentigram, derived from the centimetre–gram–second system of units and equal to 10 μg.
== Typography == Usually, a sequence of the Unicode code point {{unichar|03BC|}} followed by the Latin letter {{unichar|0067|}} should be used. However, if μ is not available it may be represented with {{unichar|0075}} or the legacy Unicode symbol {{unichar|00B5|Square Mu G}}. In Chinese, Japanese and Korean writing a fullwidth version {{unichar|338D|Square Mu G}} should be used.<ref name="Unicode-U3300">{{cite web |url=https://www.unicode.org/charts/PDF/U3300.pdf |access-date=May 24, 2019 |title=The Unicode Standard 12.0 – CJK Compatibility ❰ Range: 3300—33FF ❱ |author=Unicode Consortium |author-link=Unicode Consortium |date=2019 |website=Unicode.org |archive-date=September 30, 2023 |archive-url=https://web.archive.org/web/20230930221351/http://www.unicode.org/charts/PDF/U3300.pdf |url-status=live }}</ref>
== See also == {{wiktionary|microgram|μg|mcg}} * List of SI prefixes * Orders of magnitude (mass), listing a few items that have a mass of around 1 μg.
== References == {{reflist}}
Category:SI derived units Category:Units of mass