In the
metric system
The metric system is a system of measurement that standardization, standardizes a set of base units and a nomenclature for describing relatively large and small quantities via decimal-based multiplicative unit prefixes. Though the rules gover ...
, a microgram or microgramme is a
unit
Unit may refer to:
General measurement
* Unit of measurement, a definite magnitude of a physical quantity, defined and adopted by convention or by law
**International System of Units (SI), modern form of the metric system
**English units, histo ...
of
mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
equal to one millionth () of a
gram
The gram (originally gramme; SI unit symbol g) is a Physical unit, unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram.
Originally defined in 1795 as "the absolute Mass versus weight, weight of a volume ...
. The unit symbol is μg according to the
International System of Units
The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official s ...
(SI); the recommended symbol in the United States and United Kingdom when communicating medical information is mcg. In μg, the prefix symbol for
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 (10−6). It comes from the Ancient Greek, Greek word (), meaning "small".
It is the ...
is the Greek letter
μ (mu).
Abbreviation and symbol confusion
When the Greek lowercase "μ" (mu) is typographically unavailable, it is occasionally – although not properly – replaced by the Latin lowercase "u".
The United States–based
Institute for Safe Medication Practices (ISMP) and the U.S.
Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...
(FDA) recommend that the symbol μg should not be used when communicating medical information due to the risk that the prefix
μ (micro-) might be misread as the prefix
m (milli-), resulting in a thousandfold overdose. The ISMP recommends the non-
SI symbol mcg instead. However, the abbreviation mcg is also the symbol for an obsolete
centimetre–gram–second system of units
The centimetre–gram–second system of units (CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are unamb ...
unit of measure known as millicentigram, which is equal to 10 μg.
Gamma (symbol:
γ) is a deprecated non-SI unit of
mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
equal to 1 μg.
NIST Handbook 133 - 2018Appendix E. General Tables of Units of Measurement, page 159 (17)
/ref>
A fullwidth version of the "microgram" symbol is encoded by Unicode
Unicode or ''The Unicode Standard'' or TUS is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 16.0 defines 154,998 Char ...
at code point for use in CJK contexts.
See also
* List of SI prefixes
* Orders of magnitude (mass)
To help compare different ''orders of magnitude'', the following lists describe various ''mass'' levels between 10−67 kg and 1052 kg. The least massive thing listed here is a graviton, and the most massive thing is the observable universe ...
, listing a few items that have a mass of around 1 μg.
References
{{reflist
SI derived units
Units of mass