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''Micro'' (Greek letter μ ( U+03BC) or the legacy symbol µ (U+00B5)) is a
unit prefix A unit prefix is a specifier or mnemonic that is prepended to units of measurement to indicate multiples or fractions of the units. Units of various order of magnitude, sizes are commonly formed by the use of such prefixes. The Metric prefix, prefi ...
in the
metric system The metric system is a system of measurement that succeeded the Decimal, decimalised system based on the metre that had been introduced in French Revolution, France in the 1790s. The historical development of these systems culminated in the d ...
denoting a factor of 10−6 (one
millionth One millionth is equal to 0.000 001, or 1 x 10−6 in scientific notation. It is the reciprocal of a million, and can be also written as . Units using this fraction can be indicated using the prefix "micro-" from Greek, meaning "small". Numbers o ...
). Confirmed in 1960, the prefix comes from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
('), meaning "small". The symbol for the prefix is the
Greek letter The Greek alphabet has been used to write the Greek language since the late 9th or early 8th century BCE. It is derived from the earlier Phoenician alphabet, and was the earliest known alphabetic script to have distinct letters for vowels as w ...
μ ( mu). It is the only SI prefix which uses a character not from the
Latin alphabet The Latin alphabet or Roman alphabet is the collection of letters originally used by the ancient Romans to write the Latin language. Largely unaltered with the exception of extensions (such as diacritics), it used to write English and the o ...
. "mc" is commonly used as a prefix when the character "μ" is not available; for example, "mcg" commonly denotes a microgram. This may be ambiguous in rare circumstances in that ''mcg'' could also be read as a ''micrigram'', i.e. 10−14 g; however the prefix '' micri'' is not standard, nor widely known, and is considered obsolete. The letter u, instead of μ, was allowed by an
ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...
document, but that document has been withdrawn in 2001, however DIN 66030:2002 still allows this substitution.


Examples

* Typical
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
are 1 to 10
micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
s (1–10 µm) in diameter. *
Eukaryotic cells Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
are typically 10 to 100 micrometres in diameter.


Symbol encoding in character sets

The official symbol for the
SI prefix 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. E ...
''micro'' is a Greek lowercase mu (μ). For reasons stemming from its design,
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...
has two different character codes for the letter, with slightly different appearance in some fonts, although most fonts use the same
glyph A glyph () is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A g ...
. The micro sign (µ) is encoded in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1987), at U+00B5 (), residing at this code point also in
DEC MCS The Multinational Character Set (DMCS or MCS) is a character encoding created in 1983 by Digital Equipment Corporation (DEC) for use in the popular VT220 computer terminal, terminal. It was an 8-bit extension of ASCII that added accented character ...
(since 1983) and
ECMA-94 ISO/IEC 8859 is a joint ISO and IEC series of standards for 8-bit character encodings. The series of standards consists of numbered parts, such as ISO/IEC 8859-1, ISO/IEC 8859-2, etc. There are 15 parts, excluding the abandoned ISO/IEC 8859-12. ...
(since 1985). The Greek letter (μ) is encoded in the Greek range at U+03BC (). According to
The Unicode Consortium The Unicode Consortium (legally Unicode, Inc.) is a 501(c)(3) non-profit organization incorporated and based in Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was developed with the intent ...
, the Greek letter character is preferred,Unicode Technical Report #25
/ref> but implementations must recognize the micro sign as well. This distinction also occurs in some legacy code pages, notably
Windows-1253 Windows code page 1253 ("Greek - ANSI"), commonly known by its IANA-registered name Windows-1253 or abbreviated as cp1253, is a Microsoft Windows code page used to write modern Greek. It is not capable of supporting the older polytonic Greek. It i ...
. In circumstances in which only the
Latin alphabet The Latin alphabet or Roman alphabet is the collection of letters originally used by the ancient Romans to write the Latin language. Largely unaltered with the exception of extensions (such as diacritics), it used to write English and the o ...
is available, ISO 2955 (1974, 1983https://web.archive.org/web/20161214025341/http://www.bgu.ac.il/~averbukh/ISO_2955-1983E.pdf -->
/ref>), DIN 66030 (Vornorm 1973; 1980, 2002) and BS 6430 (1983) allow the prefix μ to be substituted by the letter u (or even U, if lowercase letters are not available), as, for example, in um for μm, or uF for μF, or in the common abbreviation UC for
microcontroller A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable i ...
(µC). Similar, capacitor values according to the
RKM code The RKM code, also referred to as "letter and numeral code for resistance and capacitance values and tolerances", "letter and digit code for resistance and capacitance values and tolerances", or informally as "R notation" is a notation to specif ...
defined in
IEC 60062 The RKM code, also referred to as "letter and numeral code for resistance and capacitance values and tolerances", "letter and digit code for resistance and capacitance values and tolerances", or informally as "R notation" is a notation to specif ...
(IEC 62) (since 1952),
EN 60062 The RKM code, also referred to as "letter and numeral code for resistance and capacitance values and tolerances", "letter and digit code for resistance and capacitance values and tolerances", or informally as "R notation" is a notation to specif ...
, DIN 40825 (1973), BS 1852 (1974), IS 8186 (1976) etc. can be written as 4u7 (or 4U7) instead of 4μ7 if the Greek letter μ is not available.


Other abbreviating conventions

In some
health care Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health profe ...
institutions, house rules deprecate the standard symbol for
microgram In the metric system, a microgram or microgramme is a unit of mass equal to one millionth () of a gram. The unit symbol is μg according to the International System of Units (SI); the recommended symbol in the United States and United Kingdom whe ...
, "μg", in prescribing or chart recording, because of the risk of giving an incorrect dose because of the misreading of poor handwriting. The two alternatives are to abbreviate as "mcg" or to write out "microgram" in full (see also
List of abbreviations used in medical prescriptions This is a list of abbreviations used in medical prescriptions, including hospital orders (the patient-directed part of which is referred to as sig codes). This list does not include abbreviations for pharmaceuticals or drug name suffixes such as C ...
). But 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), and in physical sciences academia, "μg" remains the sole official abbreviation. In medical data exchange according to the
Health Level 7 Health Level Seven or HL7 refers to a set of international standards for transfer of clinical and administrative data between software applications used by various healthcare providers. These standards focus on the application layer, which is "la ...
(HL7) standard, the μ can be replaced by u as well.


See also

*
Microgram In the metric system, a microgram or microgramme is a unit of mass equal to one millionth () of a gram. The unit symbol is μg according to the International System of Units (SI); the recommended symbol in the United States and United Kingdom whe ...
*
Microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...
*
Microsecond A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 1000 n ...
*
Microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...
* Square micrometre *
List of commonly used taxonomic affixes This is a list of common affixes used when scientifically naming species, particularly extinct species for whom only their scientific names are used, along with their derivations. *a-, an-: ''Pronunciation'': /ə/, /a/, /ən/, /an/. ''Origin'' ...


References

{{Portal bar, Physics SI prefixes