Unit of length

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A ruler, depicting two customary units of length, the centimeter and the inch Measurement unit.jpg
A ruler, depicting two customary units of length, the centimeter and the inch

A unit of length refers to 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]

Contents

Metric system

SI

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 1299792458 seconds." [4] It is approximately equal to 1.0936 yd. 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 1000 m.

Non-SI

In the centimeter–gram–second system of units, the basic unit of length is the centimeter, or 1100 of a meter. Other non-SI units are derived from decimal multiples of the meter.

NameSymbolSI value
fermifm femtometer
ångström Å100 picometers
micronμm1 micrometer
Norwegian/Swedish mil or myriameter 10,000 meters
x unit xu0.1 picometer

Imperial/U.S.

The basic unit of length in the imperial and U.S. customary systems is the yard, defined as exactly 0.9144 m by international treaty in 1959. [2] [5]

Common imperial units and U.S. customary units of length include: [6]

Marine

In addition, the following are used by sailors:

Aviation

Aviators use feet for altitude worldwide (except in Russia and China) and nautical miles for distance.[ citation needed ]

Surveying

Determination of the rod, using the length of the left foot of 16 randomly chosen people coming from church service Determination of the rute and the feet in Frankfurt.png
Determination of the rod, using the length of the left foot of 16 randomly chosen people coming from church service

Surveyors in the United States continue to use:

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 66 feet (20 m) 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:

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 propertySymbolLength, in metersReference
The classical electron radiusre2.817940285(31)×10−15 [13]
The Compton wavelength of the electronλC2.426310215(18)×10−12 [13]
The reduced Compton wavelength of the electronλC3.8615926764(18)×10−13 [14]
The Compton wavelength (or reduced Compton wavelength) of any fundamental particleλx
The Bohr radius of the hydrogen atom (Atomic unit of length)a05.291772083(19)×10−11 [13]
The reduced wavelength of hydrogen radiation1 / R9.112670505509(83)×10−8 [13]
The Planck length 𝓁P1.616199(97)×10−35 [15]
Stoney unit of lengthlS1.381×10−35
Quantum chromodynamics (QCD) unit of lengthlQCD2.103×10−16
Natural units based on the electronvolt1 eV−11.97×10−7

Archaic

Archaic units of distance include:

Informal

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:

Other

Horse racing and other equestrian activities keep alive:

See also

Related Research Articles

<span class="mw-page-title-main">Furlong</span> Unit of length equal to 660 feet or about 201 metres

A furlong is a measure of distance in imperial units and United States customary units equal to one-eighth of a mile, equivalent to any of 660 feet, 220 yards, 40 rods, 10 chains, or approximately 201 metres. It is now mostly confined to use in horse racing, where in many countries it is the standard measurement of race lengths, and agriculture, where it is used to measure rural field lengths and distances.

<span class="mw-page-title-main">Inch</span> Unit of length

The inch is a unit of length in the British Imperial and the United States customary systems of measurement. It is equal to 1/36 yard or 1/12 of a foot. Derived from the Roman uncia ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb.

<span class="mw-page-title-main">Imperial units</span> System of measurements

The imperial system of units, imperial system or imperial units is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed through a series of Weights and Measures Acts and amendments.

<span class="mw-page-title-main">Metre</span> SI unit of length

The metre is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second, where the second is defined by a hyperfine transition frequency of caesium.

<span class="mw-page-title-main">Metrication</span> Conversion to the metric system of measurement

Metrication or metrification is the act or process of converting to the metric system of measurement. All over the world, countries have transitioned from local and traditional units of measurement to the metric system. This process began in France during the 1790s, and has persistently advanced over two centuries, accumulating into 95% of the world officially only using the modern metric system. Nonetheless, this also highlights that certain countries and sectors are either still transitioning or have chosen not to fully adopt the metric system.

<span class="mw-page-title-main">United States customary units</span> System of units of measurement commonly used in the United States

United States customary units form a system of measurement units commonly used in the United States and most U.S. territories, since being standardized and adopted in 1832. The United States customary system developed from English units that were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures evolved by 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units. Consequently, while many U.S. units are essentially similar to their imperial counterparts, there are noticeable differences between the systems.

<span class="mw-page-title-main">Metric system</span> Metre-based systems of measurement

The metric system is a decimal-based system of measurement. The current international standard for the metric system is the International System of Units, in which all units can be expressed in terms of seven base units: the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). These can be made into larger or smaller units with the use of metric prefixes.

<span class="mw-page-title-main">Chinese units of measurement</span> Traditional system of measurement used by Han Chinese

Chinese units of measurement, known in Chinese as the shìzhì, are the traditional units of measurement of the Han Chinese. Although Chinese numerals have been decimal (base-10) since the Shang, several Chinese measures use hexadecimal (base-16). Local applications have varied, but the Chinese dynasties usually proclaimed standard measurements and recorded their predecessor's systems in their histories.

<span class="mw-page-title-main">Foot (unit)</span> Customary unit of length

The foot is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, , is commonly used to represent the foot. In both customary and imperial units, one foot comprises 12 inches, and one yard comprises three feet. Since an international agreement in 1959, the foot is defined as equal to exactly 0.3048 meters.

<span class="mw-page-title-main">Metrication in the United States</span> Adoption of the metric system

Metrication is the process of introducing the International System of Units, also known as SI units or the metric system, to replace a jurisdiction's traditional measuring units. U.S. customary units have been defined in terms of metric units since the 19th century, and the SI has been the "preferred system of weights and measures for United States trade and commerce" since 1975 according to United States law. However, conversion was not mandatory and many industries chose not to convert, and U.S. customary units remain in common use in many industries as well as in governmental use. There is government policy and metric (SI) program to implement and assist with metrication, however there is major social resistance for further metrication.

The Mendenhall Order marked a decision to change the fundamental standards of length and mass of the United States from the customary standards based on those of England to metric standards. It was issued on April 5, 1893, by Thomas Corwin Mendenhall, superintendent of the United States Coast and Geodetic Survey, with the approval of the United States Secretary of the Treasury, John Griffin Carlisle. The order was issued as the Survey's Bulletin No. 26 – Fundamental Standards of Length and Mass.

A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Instances in use include the International System of Units or SI, the British imperial system, and the United States customary system.

<span class="mw-page-title-main">Link (unit)</span> Unit of length

The link, sometimes called a Gunter’s link, is a unit of length formerly used in many English-speaking countries. In US customary units modern definition, the link is exactly 66100 of a US survey foot, or exactly 7.92 inches or 20.1168 cm.


The spread of metrication around the world in the last two centuries has been met with both support and opposition.

<span class="mw-page-title-main">Metrication in the United Kingdom</span> Adoption of the metric system of measurements

Metrication is the act or process of converting to the metric system of measurement. The United Kingdom, through voluntary and mandated laws, has metricated most of government, industry, commerce, and scientific research to the metric system; however, the previous measurement system is still used in society. Imperial units as of 2024 remain mandated by law to still be used without metric units for speed and distance road signs, and the sizes of cider and beer sold by the glass, returnable milk containers and precious metals, and in some areas both measurement systems are mandated by law.

<span class="mw-page-title-main">History of measurement</span>

The earliest recorded systems of weights and measures originate in the 3rd or 4th millennium BC. Even the very earliest civilizations needed measurement for purposes of agriculture, construction and trade. Early standard units might only have applied to a single community or small region, with every area developing its own standards for lengths, areas, volumes and masses. Often such systems were closely tied to one field of use, so that volume measures used, for example, for dry grains were unrelated to those for liquids, with neither bearing any particular relationship to units of length used for measuring cloth or land. With development of manufacturing technologies, and the growing importance of trade between communities and ultimately across the Earth, standardized weights and measures became critical. Starting in the 18th century, modernized, simplified and uniform systems of weights and measures were developed, with the fundamental units defined by ever more precise methods in the science of metrology. The discovery and application of electricity was one factor motivating the development of standardized internationally applicable units.

Metrication, or the conversion to a measurement system based on the International System of Units (SI), occurred in India in stages between 1955 and 1962. The metric system in weights and measures was adopted by the Indian Parliament in December 1956 with the Standards of Weights and Measures Act, which took effect beginning 1 October 1958. The Indian Coinage Act was passed in 1955 by the Government of India to introduce decimal coinage in the country. The new system of coins became legal tender in April 1957, where the rupee consists of 100 paise. For the next five years, both the old and new systems were legal. In April 1962, all other systems were banned. This process of metrication is called "big-bang" route, which is to simultaneously outlaw the use of pre-metric measurement, metricate, reissue all government publications and laws, and change the education systems to metric.

The line was a small English unit of length, variously reckoned as 110, 112, 116, or 140 of an inch. It was not included among the units authorized as the British Imperial system in 1824.

The international yard and pound are two units of measurement that were the subject of an agreement among representatives of six nations signed on 1 July 1959: Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States. The agreement defined the yard as exactly 0.9144 meters and the avoirdupois pound as exactly 0.45359237 kilograms.

<span class="mw-page-title-main">Imperial and US customary measurement systems</span> English (pre 1824), Imperial (post 1824) and US Customary (post 1776) units of measure

The imperial and US customary measurement systems are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.

References

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  2. 1 2 Hinkelman, Edward G.; Sibylla Putzi (2005). Dictionary Of International Trade: Handbook Of The Global Trade Community. World Trade Press. p. 245. ISBN   9781885073723.
  3. Judson, Lewis Van Hagen (1960). Units of Weight and Measure (United States Customary and Metric): Definitions and Tables of Equivalents, Issue,233. U.S. Department of Commerce, National Bureau of Standards. pp. 3–4. Retrieved 16 October 2012.
  4. "17th General Conference on Weights and Measures (1983), Resolution 1" . Retrieved 2012-09-19.
  5. Donald Fenna (2002). A dictionary of weights, measures, and units . Oxford University Press. pp.  130–131. ISBN   978-0198605225 . Retrieved 8 January 2012.
  6. Cardarelli 2003 , pp. 29–30
  7. Wilks, Kevin Joseph. (1992). Metrication in Australia : a review of the effectiveness of policies and procedures in Australia's conversion to the metric system. Australia. Department of Industry, Technology, and Commerce. Canberra: Australian Govt. Pub. Service. p. 94. ISBN   0-644-24860-2. OCLC   27702954.
  8. "Metrication in Australia" (PDF).
  9. Moritz, H. (March 2000). "Geodetic Reference System 1980". Journal of Geodesy. 74 (1): 128–133. Bibcode:2000JGeod..74..128.. doi:10.1007/s001900050278. S2CID   195290884.
  10. Battat, J. B. R.; Murphy, T. W.; Adelberger, E. G. (January 2009). "The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO): Two Years of Millimeter-Precision Measurements of the Earth-Moon Range". Astronomical Society of the Pacific. 121 (875): 29–40. Bibcode:2009PASP..121...29B. doi: 10.1086/596748 . JSTOR   10.1086/596748.
  11. Geoff Brumfiel (14 Sep 2012). "The astronomical unit gets fixed: Earth–Sun distance changes from slippery equation to single number" . Retrieved 14 Sep 2012.
  12. The IAU and astronomical units, International Astronomical Union, retrieved 2008-07-05
  13. 1 2 3 4 Quinn, T.J.; Leschiutta, S.; Tavella, P. (August 2000). Recent advances in metrology and fundamental constants. Amsterdam; Washington, DC: IOS Press, 2001. Proceedings of the International School of Physics "Enrico Fermi". pp. 142–143. ISBN   9781586031671.
  14. "Compton wavelength over 2 pi". The NIST Reference on Constants, Units, and Uncertainty. NIST. Retrieved 15 October 2012.
  15. "Planck length". The NIST Reference on Constants, Units, and Uncertainty. NIST . Retrieved 15 October 2012.

Further reading