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 American ...
), 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 distance. In most systems of measurement a base unit for length is chosen, from which all other units are derived. In the Interna ...
in the
International System of Units
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 ...
(SI) equalling (SI standard prefix "
micro-
''Micro'' (Greek letter μ ( U+03BC) or the legacy symbol µ (U+00B5)) 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 ...
" = ); 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 pref ...
(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
Measurement is the quantification of 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 determining how large or small a physical quantity is as compared ...
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 around ...
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 micrometres in length, bacteria were among ...
,
and for grading
wool
Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool.
As ...
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 pairs, which ...
, 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 among ...
* 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,
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 co ...
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 mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool.
As ...
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 fo ...
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 pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...
(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 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 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
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. In
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 ...
, there is also a micro sign with the
code point
In character encoding terminology, a code point, codepoint or code position is a numerical value that maps to a specific character. Code points usually represent a single grapheme—usually a letter, digit, punctuation mark, or whitespace—but ...
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 intentio ...
, 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
Character or Characters 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 The ...
.
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 pre ...
*
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 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 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
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