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The micrometre ( international spelling as used by the
International Bureau of Weights and Measures The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organisation, through which its 59 member-states act together on measurement standards in four areas: chemistry, ...
; SI symbol: μm) or micrometer (
American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the two most notable variations being British and America ...
), also commonly known as a micron, is an
SI derived unit SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI). They are either dimensionless or can be expressed as a product of one or more of the base units, possibly scaled by an ...
of
length Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Internati ...
equalling (SI standard prefix "
micro- Micro- (Greek letter μ or legacy micro symbol µ) 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 the prefix comes from th ...
" = 10−6); that is, one millionth of a
metre The metre (Commonwealth spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure", and cognate with Sanskrit , meaning "measured") is the base unit of length in the Internation ...
(or one thousandth of a
millimetre The millimetre (international spelling; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length. Therefore, there are one thousand mill ...
, 0.001 mm, or about 0.000039 
inch Measuring tape with inches The inch (symbol: in or ″) is a unit of length in the (British) imperial and United States customary systems of measurement. It is equal to yard or of a foot. Derived from the Roman uncia ("twelfth"), the word ...
). The next smallest common SI unit is the
nanometre The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American spelling) is a unit of length in the metric system, equal to one billionth (short scale) of a metre ( m). One ...
, equivalent to one one-thousandth of a micrometre, or one billionth of a metre ( m). The micrometre is a common unit of
measurement ' Measurement is the numerical quantification of the attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measurement are dependent on the context and discipline. In natural scien ...
for
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...
s of
infrared radiation Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from the nomi ...
as well as sizes of biological
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
and
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres ...
, and for grading
wool Wool is the textile fiber obtained from sheep and other animals, including cashmere and mohair from goats, qiviut from muskoxen, hide and fur clothing from bison, angora from rabbits, and other types of wool from camelids. Wool consists of p ...
by the diameter of the fibres. The width of a single human hair ranges from approximately 20 to 200 μm. The longest human chromosome is approximately 10 μm in length.


Examples

Between 1 μm and 10 μm: * 1–10 μm – length of a typical
bacterium Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres ...
* 10 μm – Size of fungal hyphae * 5 μm – length of a typical human
spermatozoon A spermatozoon (pronounced , alternate spelling spermatozoön; plural spermatozoa; from grc, σπέρμα ("seed") and grc, ζῷον ("living being")) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozo ...
's head * 3–8 μm – width of strand of spider web silk * about 10 μm – size of a fog,
mist Mist is a phenomenon caused by small droplets of water suspended in air. Physically, it is an example of a dispersion. It is most commonly seen where warm, moist air meets sudden cooling, such as in exhaled air in the winter, or when throwing w ...
, or
cloud In meteorology, a cloud is an aerosol consisting of a visible mass of minute liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may compose ...
water droplet Between 10 μm and 100 μm: * about 10–12 μm – thickness of plastic wrap (cling wrap) * 10 to 55 μm – width of
wool Wool is the textile fiber obtained from sheep and other animals, including cashmere and mohair from goats, qiviut from muskoxen, hide and fur clothing from bison, angora from rabbits, and other types of wool from camelids. Wool consists of p ...
fibre * 17 to 181 μm – diameter of human hairThe
diameter In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for th ...
of human hair ranges from 17 to 181 μm.
* 70 to 180 μm – thickness of paper


SI standardization

The term ''micron'' and the symbol μ were officially accepted for use in isolation to denote the micrometre in 1879, but officially revoked by the
International System of Units International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * ''International'' (Kevin Michael album), 2011 * ''International'' (New Order album), 2002 * ''International'' (The Three ...
(SI) in 1967.BIPM - Resolution 7 of the 13th CGPM 1967/68)
"Abrogation of earlier decisions (micron, new candle.)"
This became necessary because the older usage was incompatible with the official adoption of the unit prefix ''micro-'', denoted μ, during the creation of the SI in 1960. In the SI, the systematic name ''micrometre'' became the official name of the unit, and μm became the official unit symbol. Additionally, in
American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English is the most influential form of ...
, the use of "micron" helps differentiate the unit from the
micrometer A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for accurate measurement of components in mechanical engineering and machining as well as most mechanical trades, along with othe ...
, a measuring device, because the unit's name in mainstream
American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the two most notable variations being British and America ...
is a
homograph A homograph (from the el, ὁμός, ''homós'', "same" and γράφω, ''gráphō'', "write") is a word that shares the same written form as another word but has a different meaning. However, some dictionaries insist that the words must also s ...
of the device's name. In spoken English, they may be distinguished by pronunciation, as the name of the measuring device is often stressed on the second syllable ( ), whereas the systematic pronunciation of the unit name, in accordance with the convention for pronouncing SI units in English, places the stress on the first syllable ( ). The plural of ''micron'' is normally ''microns'', though ''micra'' was occasionally used before 1950.


Symbol

The official symbol for the
SI prefix A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The prefix '' ...
''micro-'' is a Greek lowercase mu. In
Unicode Unicode 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 is maintained by the Unicode Consortium, and , it has a total of (th ...
, there is also a micro sign with the
code point In character encoding terminology, a code point or code position is any of the numerical values that make up the ''codespace''. Many code points represent single characters but they can also have other meanings, such as for formatting. For examp ...
U+00B5 (μ), distinct from the code point U+03BC (μ) of the Greek letter lowercase mu. 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 intention of ...
, the Greek letter character is preferred, but implementations must recognize the micro sign as well. Most fonts use the same
glyph In typography, a glyph is an elemental symbol within an agreed set of symbols, intended to represent a readable character for the purposes of writing. Glyphs are considered to be unique marks that collectively add up to the spelling of a word ...
for the two
characters Character(s) may refer to: Arts, entertainment, and media Literature * ''Character'' (novel), a 1936 Dutch novel by Ferdinand Bordewijk * ''Characters'' (Theophrastus), a classical Greek set of character sketches attributed to Theophrastus Musi ...
.


See also

*
Metric prefix A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The prefix '' ...
*
Metric system A metric system is a system of measurement that succeeded the decimalised system based on the metre introduced in France in the 1790s. The historical development of these systems culminated in the definition of the International System of Unit ...
*
Orders of magnitude (length) The following are examples of orders of magnitude for different lengths. __TOC__ Overview Detailed list To help compare different orders of magnitude, the following list describes various lengths between 1.6 \times 10^ metres and 10^ ...
*
Wool measurement A micron (micrometre) is the measurement used to express the diameter of wool fibre. Fine wool fibers have low micron value. Fibre diameter is the most important characteristic of wool in determining its value. Every fleece comprises a very wide ...


Notes and references


External links

* {{SI units of length
Units of length Length Length {{CatAutoTOC ...
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