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 ...
;
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 American ...
), also commonly known as a micron, is a unit of
length in the
International System of Units (SI) equalling (SI standard prefix "
micro-" = ); that is, one millionth of a
metre
The metre ( British spelling) or meter ( American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its pre ...
(or one thousandth of a
millimetre, , or about ).
The nearest smaller common SI unit is the
nanometre, 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 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, tr ...
s of
infrared radiation 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:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
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 micrometres in length, bacteria were am ...
,
and for grading
wool by the diameter of the fibres.
The width of a single human hair ranges from approximately 20 to . The longest human chromosome,
chromosome 1, 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 biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
* 3–8 μm – width of strand of
spider web silk
* 5 μm – length of a typical human
spermatozoon's head
* 10 μm – Size of
fungal hyphae
* about 10 μm – size of a
fog
Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
,
mist, or
cloud
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...
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 fibre
* 17 to 181 μm – diameter of human hair
[The ]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 of the circle. Both definitions are also valid f ...
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 (SI) in 1967.
[BIPM - Resolution 7 of the 13th CGPM 1967/68)](_blank)
"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 varieties of the English language native to the United States. English is the most widely spoken language in the United States and in most circumstances ...
, the use of "micron" helps differentiate the unit from the
micrometer Micrometer can mean:
* Micrometer (device), used for accurate measurements by means of a calibrated screw
* American spelling of micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
, 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 American ...
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 ''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 U+00B5 (µ), distinct from the code point U+03BC (μ) of the Greek letter lowercase mu. According to the
Unicode Consortium, the Greek letter character is preferred,
but implementations must recognize the micro sign as well. Most fonts use the same
glyph 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 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 ...
*
Orders of magnitude (length)
*
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 ...
Notes and references
External links
*
{{SI units of length
Metre
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