In the
metric system
The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Intern ...
, a microgram or microgramme is a
unit
Unit may refer to:
Arts and entertainment
* UNIT, a fictional military organization in the science fiction television series ''Doctor Who''
* Unit of action, a discrete piece of action (or beat) in a theatrical presentation
Music
* ''Unit'' (a ...
of
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...
equal to one millionth () of a
gram
The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram.
Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
. The unit symbol is μg according to the
International System of Units
The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...
(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 ( U+03BC) or the legacy symbol µ (U+00B5)) is a unit prefix in the metric system denoting a factor of 10−6 (one millionth). Confirmed in 1960, the prefix comes from the Greek ('), meaning "small".
The symbol for ...
is the Greek letter
μ (mu).
Abbreviation and symbol confusion
When the Greek lowercase "μ" (mu) in the symbol μg 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 federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
(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 (abbreviated 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 ...
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 property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...
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, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...
at code point for use in CJK contexts.
See also
* List of SI prefixes
* Orders of magnitude (mass), listing a few items that have a mass of around 1 μg.
References
{{reflist
SI derived units
Units of mass