Unit of length: Difference between revisions
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[[File:Measurement_unit.jpg |thumb|right|A ruler, depicting two customary units of length, the centimeter and the inch]] | [[File:Measurement_unit.jpg |thumb|right|A ruler, depicting two customary units of length, the centimeter and the inch]] | ||
A '''unit of length''' | A '''unit of length''' is any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the [[metric system|metric units]], used in every country globally. In the United States the [[U.S. customary units]] are also in use. British [[Imperial units]] are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into [[International System of Units|SI]] and non-SI units.<ref>{{cite book|last=Cardarelli|first=François|title=Encyclopaedia of Scientific Units, Weights, and Measures: Their SI Equivalences and Origins|url=https://archive.org/details/encyclopaediaofs0000card|url-access=registration|year=2003|publisher=Springer|isbn=9781852336820 }}</ref><ref name=Hinkelman>{{cite book|last=Hinkelman|first=Edward G.|author2=Sibylla Putzi |title=Dictionary Of International Trade: Handbook Of The Global Trade Community|year=2005|publisher=World Trade Press|page=245|isbn=9781885073723}}</ref><ref>{{cite book|last=Judson|first=Lewis Van Hagen|title=Units of Weight and Measure (United States Customary and Metric): Definitions and Tables of Equivalents, Issue,233|year=1960|pages=3–4|publisher=U.S. Department of Commerce, National Bureau of Standards |url=https://books.google.com/books?id=Mialg1senzMC&q=Units+of+Weight+and+Measure+%28United+States+Customary+and+Metric%29 |access-date=16 October 2012}}</ref> | ||
== History == | == History == | ||
| Line 48: | Line 48: | ||
==Imperial/U.S.== | ==Imperial/U.S.== | ||
{{main article|Imperial units|United States customary units|English units# | {{main article|Imperial units|United States customary units|English units of measurement#Length}} | ||
The basic unit of length in the imperial and U.S. customary systems is the [[yard]], defined as exactly {{val|0.9144|u=m}} by international treaty in 1959.<ref name=Hinkelman/><ref name="Fenna2002">{{cite book|author=Donald Fenna|title=A dictionary of weights, measures, and units|url=https://archive.org/details/dictionaryofweig0000fenn|url-access=registration|access-date=8 January 2012|date=2002|publisher=Oxford University Press|isbn=978-0198605225|pages=[https://archive.org/details/dictionaryofweig0000fenn/page/130 130]–131}}</ref> | The basic unit of length in the imperial and U.S. customary systems is the [[yard]], defined as exactly {{val|0.9144|u=m}} by international treaty in 1959.<ref name=Hinkelman/><ref name="Fenna2002">{{cite book|author=Donald Fenna|title=A dictionary of weights, measures, and units|url=https://archive.org/details/dictionaryofweig0000fenn|url-access=registration|access-date=8 January 2012|date=2002|publisher=Oxford University Press|isbn=978-0198605225|pages=[https://archive.org/details/dictionaryofweig0000fenn/page/130 130]–131}}</ref> | ||
| Line 75: | Line 76: | ||
===Australian building trades=== | ===Australian building trades=== | ||
The Australian building trades adopted the [[metric system]] in 1966 and the units used for measurement of length are [[meters]] (m) and [[millimeters]] (mm). [[Centimeters]] (cm) are avoided as they cause confusion when reading [[plans]]. For example, the length two and a half meters is usually recorded as 2500 mm or 2.5 m; it would be considered non-standard to record this length as 250 cm.<ref>{{Cite book|last=Wilks, Kevin Joseph. | The Australian building trades adopted the [[metric system]] in 1966 and the units used for measurement of length are [[meters]] (m) and [[millimeters]] (mm). [[Centimeters]] (cm) are avoided as they cause confusion when reading [[plans]]. For example, the length two and a half meters is usually recorded as 2500 mm or 2.5 m; it would be considered non-standard to record this length as 250 cm.<ref>{{Cite book|last=Wilks, Kevin Joseph.|title=Metrication in Australia : a review of the effectiveness of policies and procedures in Australia's conversion to the metric system|date=1992|publisher=Australian Govt. Pub. Service|others=Australia. Department of Industry, Technology, and Commerce.|isbn=0-644-24860-2|location=Canberra|pages=94|oclc=27702954}}</ref><ref>{{Cite web|url=http://themetricmaven.com/wp-content/uploads/2012/03/Metrication-in-Australia-built-2013-06-24.pdf|title=Metrication in Australia}}</ref> | ||
===Surveyor's trade=== | ===Surveyor's trade=== | ||
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===Astronomy=== | ===Astronomy=== | ||
{{main article|Astronomical system of units}} | {{main article|Astronomical system of units}} | ||
[[Astronomy|Astronomical]] measure uses: | [[Astronomy|Astronomical]] measure uses: | ||
*[[Earth radius]] {{Earth radius}} ≈ 6,371 km<ref name="Moritz2000">{{cite journal |last=Moritz |first=H. |date=March 2000 |title=Geodetic Reference System 1980 |journal=Journal of Geodesy |volume=74 |issue=1 |pages=128–133 |doi=10.1007/s001900050278 |bibcode = 2000JGeod..74..128. |s2cid=195290884 }}</ref> | *[[Earth radius]] {{Earth radius}} ≈ 6,371 km<ref name="Moritz2000">{{cite journal |last=Moritz |first=H. |date=March 2000 |title=Geodetic Reference System 1980 |journal=Journal of Geodesy |volume=74 |issue=1 |pages=128–133 |doi=10.1007/s001900050278 |bibcode = 2000JGeod..74..128. |s2cid=195290884 }}</ref> | ||
* [[Lunar distance (astronomy)|Lunar distance]] ''LD'' ≈ {{val|384402|u=km}}.<ref name="Apache Point">{{cite journal|last1=Battat|first1=J. B. R.|last2=Murphy|first2=T. W.|last3=Adelberger|first3=E. G.|title=The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO): Two Years of Millimeter-Precision Measurements of the Earth-Moon Range|journal=Astronomical Society of the Pacific|date=January 2009|volume=121|issue=875|pages=29–40|doi=10.1086/596748|jstor=10.1086/596748|bibcode = 2009PASP..121...29B |doi-access=free}}</ref> Average distance between the center of Earth and the center of the Moon. | * [[Lunar distance (astronomy)|Lunar distance]] ''LD'' ≈ {{val|384402|u=km}}.<ref name="Apache Point">{{cite journal|last1=Battat|first1=J. B. R.|last2=Murphy|first2=T. W.|last3=Adelberger|first3=E. G.|title=The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO): Two Years of Millimeter-Precision Measurements of the Earth-Moon Range|journal=Astronomical Society of the Pacific|date=January 2009|volume=121|issue=875|pages=29–40|doi=10.1086/596748|jstor=10.1086/596748|bibcode = 2009PASP..121...29B |doi-access=free}}</ref> Average distance between the center of Earth and the center of the Moon. | ||
*[[astronomical unit]] au. Defined as {{val|149597870700|u=m}}.<ref name=Nature2012>{{cite | *[[astronomical unit]] au. Defined as {{val|149597870700|u=m}}.<ref name=Nature2012>{{cite journal | ||
| url = http://www.nature.com/news/the-astronomical-unit-gets-fixed-1.11416 | | url = http://www.nature.com/news/the-astronomical-unit-gets-fixed-1.11416 | ||
| title = The astronomical unit gets fixed: Earth–Sun distance changes from slippery equation to single number. | | title = The astronomical unit gets fixed: Earth–Sun distance changes from slippery equation to single number. | ||
| author = Geoff Brumfiel | | author = Geoff Brumfiel | ||
| journal = Nature | |||
| date = 14 Sep 2012 | | date = 14 Sep 2012 | ||
| doi = 10.1038/nature.2012.11416 | |||
| access-date = 14 Sep 2012 | | access-date = 14 Sep 2012 | ||
}}</ref> Approximately the distance between the Earth and Sun. | | url-access = subscription | ||
*[[light-year]] ly ≈ {{val|9460730472580.8|u=km}}. The distance that light travels in a [[vacuum]] in one [[Julian year (astronomy)|Julian year]].<ref name="IAUgen">{{citation| url = http://www.iau.org/public_press/themes/measuring/ | title = The IAU and astronomical units | publisher = International Astronomical Union | access-date=2008-07-05}}</ref> | }}</ref> Approximately the distance between the Earth and Sun. | ||
*[[light-year]] ly ≈ {{val|9460730472580.8|u=km}}. The distance that light travels in a [[vacuum]] in one [[Julian year (astronomy)|Julian year]].<ref name="IAUgen">{{citation | url = http://www.iau.org/public_press/themes/measuring/ | title = The IAU and astronomical units | publisher = International Astronomical Union | access-date = 2008-07-05 | archive-date = 2009-10-22 | archive-url = https://web.archive.org/web/20091022182129/http://www.iau.org/public_press/themes/measuring/ | url-status = dead }}</ref> | |||
*[[parsec]] pc ≈ {{val|30856775814671.9|u=km}} or about {{val|3.26156|u=ly}} | *[[parsec]] pc ≈ {{val|30856775814671.9|u=km}} or about {{val|3.26156|u=ly}} | ||
*[[Hubble's law#Hubble length|Hubble length]] 14.4 billion light-years or 4.55 gigaparsecs | *[[Hubble's law#Hubble length|Hubble length]] 14.4 billion light-years or 4.55 gigaparsecs | ||
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==Archaic== | ==Archaic== | ||
{{See also|English units#Length|label 1=English units of length}} | {{See also|English units of measurement#Length|label 1=English units of length}} | ||
[[Archaism|Archaic]] units of distance include: | [[Archaism|Archaic]] units of distance include: | ||
*[[cana (unit)|cana]] | *[[cana (unit)|cana]] | ||
Latest revision as of 20:02, 27 December 2025
Template:Short description Template:Use American English Script error: No such module "Unsubst".
A unit of length is any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the metric units, used in every country globally. In the United States the U.S. customary units are also in use. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.[1][2][3]
History
Metric system
SI
Template:Main article Script error: No such module "Labelled list hatnote". The base unit in the International System of Units (SI) is the meter, defined as "the length of the path travelled by light in vacuum during a time interval of <templatestyles src="Fraction/styles.css" />1⁄299792458 seconds."[4] It is approximately equal to Script error: No such module "val".. Other SI units are derived from the meter by adding prefixes, as in millimeter or kilometer, thus producing systematic decimal multiples and submultiples of the base unit that span many orders of magnitude. For example, a kilometer is Script error: No such module "val"..
Non-SI
In the centimeter–gram–second system of units, the basic unit of length is the centimeter, or <templatestyles src="Fraction/styles.css" />1⁄100 of a meter. Other non-SI units are derived from decimal multiples of the meter.
| Name | Symbol | SI value |
|---|---|---|
| fermi | fm | 1 femtometer |
| ångström | Å | 100 picometers |
| micron | μm | 1 micrometer |
| Norwegian/Swedish mil or myriameter | 10,000 meters | |
| x unit | xu | 0.1 picometer |
Imperial/U.S.
The basic unit of length in the imperial and U.S. customary systems is the yard, defined as exactly Script error: No such module "val". by international treaty in 1959.[2][5]
Common imperial units and U.S. customary units of length include:[6]
- thou or mil (<templatestyles src="Fraction/styles.css" />1⁄1000 of an inch)
- inch (Script error: No such module "val".)
- foot (12 inches, 0.3048 m)
- yard (3 feet, 0.9144 m)
- (terrestrial) mile (5280 feet, or 1760 yards 1609.344 m)
- (land) league Script error: No such module "convert".
Marine
In addition, the following are used by sailors:
- fathom (for depth; only in non-metric countries) (2 yards = 1.8288 m)
- nautical mile (one minute of arc of latitude = Script error: No such module "val".)
Aviation
Aviators use feet for altitude worldwide (except in Russia and China) and nautical miles for distance.Script error: No such module "Unsubst".
Surveying
Surveyors in the United States continue to use:
- chain (22 yards, or Script error: No such module "val".)
- rod (also called pole or perch) (quarter of a chain, 5<templatestyles src="Fraction/styles.css" />1⁄2 yards, or Script error: No such module "val".)
Australian building trades
The Australian building trades adopted the metric system in 1966 and the units used for measurement of length are meters (m) and millimeters (mm). Centimeters (cm) are avoided as they cause confusion when reading plans. For example, the length two and a half meters is usually recorded as 2500 mm or 2.5 m; it would be considered non-standard to record this length as 250 cm.[7][8]
Surveyor's trade
American surveyors use a decimal-based system of measurement devised by Edmund Gunter in 1620. The base unit is Gunter's chain of Script error: No such module "convert". which is subdivided into 4 rods, each of 16.5 ft or 100 links of 0.66 feet. A link is abbreviated "lk", and links "lks", in old deeds and land surveys done for the government.
Science
Astronomy
Astronomical measure uses:
- Earth radius R🜨 ≈ 6,371 km[9]
- Lunar distance LD ≈ Script error: No such module "val"..[10] Average distance between the center of Earth and the center of the Moon.
- astronomical unit au. Defined as Script error: No such module "val"..[11] Approximately the distance between the Earth and Sun.
- light-year ly ≈ Script error: No such module "val".. The distance that light travels in a vacuum in one Julian year.[12]
- parsec pc ≈ Script error: No such module "val". or about Script error: No such module "val".
- Hubble length 14.4 billion light-years or 4.55 gigaparsecs
Physics
In atomic physics, sub-atomic physics, and cosmology, the preferred unit of length is often related to a chosen fundamental physical constant, or combination thereof. This is often a characteristic radius or wavelength of a particle. Some common natural units of length are included in this table:
| Atomic property | Symbol | Length, in meters | Reference |
|---|---|---|---|
| The classical electron radius | re | Script error: No such module "val". | [13] |
| The Compton wavelength of the electron | λC | Script error: No such module "val". | [13] |
| The reduced Compton wavelength of the electron | Template:StrikethroughC | Script error: No such module "val". | [14] |
| The Compton wavelength (or reduced Compton wavelength) of any fundamental particle | Template:Strikethroughx | ||
| The Bohr radius of the hydrogen atom (Atomic unit of length) | a0 | Script error: No such module "val". | [13] |
| The reduced wavelength of hydrogen radiation | 1 / R∞ | Script error: No such module "val". | [13] |
| The Planck length | 𝓁P | Script error: No such module "val". | [15] |
| Stoney unit of length | lS | Script error: No such module "val". | |
| Quantum chromodynamics (QCD) unit of length | lQCD | Script error: No such module "val". | |
| Natural units based on the electronvolt | 1 eV−1 | Script error: No such module "val". |
Archaic
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Archaic units of distance include:
- cana
- cubit
- rope
- league
- li (China)
- pace (the "double pace" of about 5 feet used in Ancient Rome)
- verst (Russia)
Informal
Script error: No such module "Labelled list hatnote". In everyday conversation, and in informal literature, it is common to see lengths measured in units of objects of which everyone knows the approximate width. Common examples are:
- Double-decker bus (9.5–11 meters in length)
- American football field (100 yards in length)
- Thickness of a human hair (around 80 micrometers)
Other
Horse racing and other equestrian activities keep alive:
- furlong = Script error: No such module "convert".
- horse length ≈ Script error: No such module "convert".
See also
- Template:Section link
- List of examples of lengths
- Template:Section link
- Medieval weights and measures
- Orders of magnitude (length)
- System of measurement
- Units of measurement
References
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Further reading
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