micron
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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 List of intergovernmental organizations, intergovernmental organisation, through which its 59 member-states act together on measur ...
; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of
length Length is a measure of distance. In the International System of Quantities, length is a quantity with Dimension (physical quantity), dimension distance. In most Measurement system, systems of measurement a Base unit (measurement), base unit f ...
in the
International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms and initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wid ...
(SI) equalling (SI standard prefix "
micro- ''Micro'' (Greek letter μ (Unicode, U+03BC) or the legacy symbol µ (U+00B5)) is a metric prefix, unit prefix in the metric system denoting a factor of 10−6 (one millionth). Confirmed in 1960, the prefix comes from the Ancient Greek, Greek (' ...
" = ); that is, one millionth of a
metre The metre (British English, British spelling) or meter (American English, American spelling; American and British English spelling differences#-re, -er, see spelling differences) (from the French unit , from the Greek language, Greek noun , "m ...
(or one thousandth of a
millimetre file:EM Spectrum Properties edit.svg, 330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter. The millimetre (American and British Eng ...
, , or about ). The nearest smaller common SI unit is the
nanometre 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
, equivalent to one thousandth of a micrometre, one millionth of a millimetre or one billionth of a metre (). The micrometre is a common unit of
measurement Measurement is the quantification (science), quantification of variable and attribute (research), attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determi ...
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 (waves), phase on the wave, such as two adjac ...
s of
infrared radiation Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
as well as sizes of biological cells and
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 micrometre The micrometre (Amer ...
, and for grading
wool Wool is the textile fibre obtained from sheep and other mammal, mammals, especially goat, goats, rabbit, rabbits, and camelid, camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties ...
by the diameter of the fibres. The width of a single human hair ranges from approximately 20 to . The longest human chromosome,
chromosome 1 Chromosome 1 is the designation for the largest human chromosome. Humans have two copies of chromosome 1, as they do with all of the autosomes, which are the non- sex chromosomes. Chromosome 1 spans about 249 million nucleotide base pair A ba ...
, is approximately in length.


Examples

Between 1 μm and 10 μm: * 1–10 μm – length of a typical
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
* 3–8 μm – width of strand of spider web silk * 5 μm – length of a typical human
spermatozoon A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell (biology), cell, or moving form of the ploidy, haploid cell (biology), cell that is the male gamete. A spermatozoon Fertilization, joins an ovum to form a zygote. (A zygote ...
's head * 10 μm – Size of fungal hyphae * about 10 μm – size of a fog,
mist Mist is a phenomenon caused by small droplets of water suspended in the cold air, usually by condensation. Physically, it is an example of a Dispersion (chemistry), dispersion. It is most commonly seen where water vapor in warm, moist air meets ...
, or
cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid drop (liquid), droplets, ice crystals, frozen crystals, or other particulates, particles suspended in the atmosphere of a planetary body or similar space. ...
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 fibre obtained from sheep and other mammal, mammals, especially goat, goats, rabbit, rabbits, and camelid, camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties ...
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 center of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...
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 The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms and initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wid ...
(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, sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. English is the Languages of the United States, most widely spoken lan ...
, the use of "micron" helps differentiate the unit from the micrometer, a measuring device, because the unit's name in mainstream American spelling 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 ...
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 The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms and initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wid ...
''micro-'' is a Greek lowercase mu. In
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, ...
, there is also a micro sign with the
code point In character encoding Character encoding is the process of assigning numbers to Graphics, graphical character (computing), characters, especially the written characters of Language, human language, allowing them to be Data storage, stored, D ...
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, Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was d ...
, the Greek letter character is preferred, but implementations must recognize the micro sign as well. 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 ...
for the two characters.


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 pr ...
*
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 ...
*
Orders of magnitude (length) The following are examples of orders of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the r ...
*
Wool measurement A micron (micrometre) is the measurement used to express the diameter of wool fibre. Fine wool fibers have a low micron value. Fibre diameter is the most important characteristic of wool in determining its value. Every fleece comprises a very w ...


Notes and references


External links

* {{SI units of length Metre -06