''Micro'' (

Greek letter The Greek alphabet has been used to write the Greek language since the late 9th or early 8th century BC. It was derived from the earlier Phoenician alphabet, and is the earliest known alphabetic script to systematically write vowels as wel ...

μ, mu, non- italic) is a

unit prefix A unit prefix is a specifier or mnemonic that is added to the beginning of a unit 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 ...

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 ...

denoting a factor of one millionth (10⁻⁶). It comes from the

Greek Greek may refer to: 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 of all kno ...

word (), meaning "small". It is the only SI prefix which uses a character not from the

Latin alphabet The Latin alphabet, also known as the Roman alphabet, is the collection of letters originally used by the Ancient Rome, ancient Romans to write the Latin language. Largely unaltered except several letters splitting—i.e. from , and from � ...

. In

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 ...

, the symbol is represented by or the legacy symbol . When

characters are not available, the letter "u" is sometimes used instead of "μ". The prefix "mc" is also commonly used; for example, "mcg" denotes a microgram.

Examples

* Typical

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

are 1 to 10 μm in diameter. *

Human hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and f ...

typically varies in diameter from 17 to 181 μm. * Eukaryotic cells are typically 10 to 100 μm in diameter.

Symbol encoding in character sets

The official symbol for the

SI prefix 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 st ...

''micro'' is a Greek lowercase mu (μ). For reasons stemming from its design,

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 ...

. () is in the "Latin-1 Supplement" range identical to

ISO/IEC 8859-1 ISO/IEC 8859-1:1998, ''Information technology—8-bit single-byte coded graphic character sets—Part 1: Latin alphabet No. 1'', is part of the ISO/IEC 8859 series of ASCII-based standard character encodings, first edition published in 1987 ...

(since 1987), 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 terminal. It was an 8-bit extension of ASCII that added accented characters, currency symb ...

(since 1983) and ECMA-94 (since 1985). () is in the Greek range. According to The Unicode Consortium, the Greek letter character is preferred,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

is available,

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

2955 (since 1974, withdrawn 2001
/ref>), Deutsches Institut für Normung, DIN 66030 (since 1980) and BS 6430 (since 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 (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...

(μC). Similarly, 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 speci ...

defined in IEC 60062 (since 1952) can be written as 4u7 (or 4U7) instead of 4μ7 if the Greek letter μ is not available. The CJK Compatibility block contains square forms of some Japanese

katakana is a Japanese syllabary, one component of the Japanese writing system along with hiragana, kanji and in some cases the Latin script (known as rōmaji). The word ''katakana'' means "fragmentary kana", as the katakana characters are derived fr ...

measure and currency units. corresponds to .

Other abbreviating conventions

In some

health care Health care, or healthcare, is the improvement or maintenance of health via the preventive healthcare, prevention, diagnosis, therapy, treatment, wikt:amelioration, amelioration or cure of disease, illness, injury, and other disability, physic ...

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 wh ...

, "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 ...

). The alternative abbreviation 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. 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 Physical science is a branch of natural science that studies non-living systems, in contrast to life science. It in turn has many branches, each referred to as a "physical science", together is called the "physical sciences". Definition ...

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.

References

{{Portal bar, Physics SI prefixes

Examples

Symbol encoding in character sets

Other abbreviating conventions

See also

References