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The '''International System of Units'''(abbreviated '''SI''' from {{lang-fr|Système international d'unités}}<ref>[http://www.bipm.org/en/CGPM/db/11/12/ Resolution of the International Bureau of Weights and Measures establishing the International System of Units]</ref>) is Unitsis the modern form of the [[metric system]] and is generally a system of [[units of measurement]] devised around seven [[SI base unit|base units]] and the convenience of the number ten. The older metric system included several groups of units. The SI was established in 1960, based on the [[Mks system of units|metre-kilogram-second]] system, rather than the [[Centimetre–gram–second system of units|centimetre-gram-second]] system, which, in turn, had a few variants. The SI is declared as an evolving system, thus prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses, and as the precision of measurements improves.

SI is the world's most widely used [[Systems of measurement|system of measurement]], which is used both in everyday [[commerce]] and in [[science]].<ref>[http://www.bipm.org/en/si/base_units/ Official BIPM definitions]</ref><ref>[http://www.physics.nist.gov/cuu/Units/introduction.html Essentials of the SI: Introduction]</ref><!--English units are still used in some scientific applications, but note also that parsecs in astronomy, calories and mmHg in the medical sciences, and electron volts in physics are not part of the specific system of units known as SI, to just scratch the surface--><ref>An extensive presentation of the SI units is maintained on line by [http://www.physics.nist.gov/cuu/Units/units.html NIST], including a [http://www.physics.nist.gov/cuu/Units/SIdiagram.html diagram] of the interrelations between the derived units based upon the SI units. Definitions of the basic units can be found on this siteat the sites bottom, as well as the [http://physics.nist.gov/cuu/Constants/codata.pdf CODATA report] listing values for special constants such as the [[electric constant]], the [[magnetic constant]] and the [[speed of light]], all of which have defined values as a result of the definition of the metre and ampere.<blockquote>In the International System of Units (SI) (BIPM, 2006), the definition of the metre fixes the speed of light in vacuum ''c''₀, the definition of the ampere fixes the magnetic constant (also called the permeability of vacuum) ''μ''₀, and the definition of the mole fixes the molar mass of the carbon 12 atom ''M''(¹²C) to have the exact values given in the bottom table [Table 1, p.7]. Since the electric constant (also called the permittivity of vacuum) is related to ''μ''₀ by ''ε''₀ = 1/''μ''₀''c''₀², it too is known exactly.</blockquote>&nbsp;– CODATA report</ref> The system has been nearly [[Metrication|globally adopted]] with the United States being the only industrialized nation that does not mainly use the metric system in its commercial and standards activities.<ref>{{cite web|url = http://en.wikipedia.org/w/index.php?title=International_System_of_Units&action=edit|title = Appendix G : Weights and Measures|work = [[The World Factbook]]|publisher = [[Central Intelligence Agency]]|accessdate =3 September 2011}}</ref> The United Kingdom has officially [[Metrication in the United Kingdom|partially adopted metrication]], with no intention of replacing [[imperial units]] entirely. [[Metrication in Canada|Canada]] has adopted it for many purposes but [[Imperial units|imperial]]/[[United States customary units|US]] units are still legally permitted and remain in common use throughout many sectors of Canadian society, particularly in the retail food, buildings trades, and railways sectors.<ref>''[http://laws-lois.justice.gc.ca/eng/acts/W-6/page-14.html/ Weights and Measures Act]''</ref><ref>''[http://laws-lois.justice.gc.ca/eng/acts/W-6/page-2.html#h-4/ Weights and Measures Act], accessed January 2012, Act current to 18 January 2012. Canadian units (5) The Canadian units of measurement are as set out and defined in Schedule II, and the symbols and abbreviations therefor are as added pursuant to subparagraph 6(1)(b)(ii).</ref>

The [[metric system]] was conceived by a group desire for international cooperation on metrology led to the signing in 1875 of scientists (among themthe Metre Convention, [[Antoine Lavoisier|Antoine-Laurent Lavoisier]], who is known as a treaty that established three international organizations to oversee the "father keeping of modern chemistry") who had been commissioned by the ''[[Assemblee Nationale|Assemblée nationale]]'' metric standards:* General Conference on Weights and [[Louis XVI]] of France Measures – a meeting every four to create a unified and rational system six years of measures.On 1 August 1793, the National Convention adopted the new decimal ''[[metre]]'' with a provisional length as well as the other decimal units with preliminary definitions delegates from all member states;* International Bureau of Weights and terms. On 7 April 1795 (''Loi du 18 germinal, Measures - an III'') the terms ''[[gram]]me'' international metrology centre in France; and ''[[kilogram]]me'' replaced the former terms ''gravet'' (correctly ''milligrave'') * International Committee for Weights and ''[[grave (unit)|grave]]'' and on 22 June 1799, after [[Pierre Méchain]] and [[Jean-Baptiste Delambre]] completed their survey, Measures —an administrative committee that meets annually at the definitive standard metre was deposited in the French National Archives. On 10 December 1799 (a month after [[coup of 18 Brumaire|Napoleon's coup d'état]]), the metric system was definitively adopted in FranceBIPM.

The desire for international cooperation on [[metrology]] led to history of the signing in 1875 metric system has seen a number of variations, and has spread around the [[Metre Convention]]world, a treaty that established three international organizations to oversee replace many traditional measurement systems. At the keeping end of World War II, a number of different systems of measurement were still in use throughout the world. Some of these systems were metric standards:* [[-system variations, whereas others were based on customary systems. It was recognised that additional steps were needed to promote a worldwide measurement system. As a result, the 9th General Conference on Weights and Measures]] (''Conférence générale des poids et mesures'' or CGPM) – a meeting every four to six years of delegates from all member states;* [[International Bureau of Weights and Measures]] (''Bureau international des poids et mesures'' or BIPM) – an international metrology centre at [[Sèvres]] , in France; and* [[1948, asked the International Committee for Weights and Measures]] (''Comité to conduct an international des poids et mesures'' or CIPM)—an administrative committee that meets annually at study of the BIPMmeasurement needs of the scientific, technical, and educational communities.

The [[Metric system#History|history of Based on the metric system]] has seen a number findings of variationsthis study, and has spread around the world, 10th CGPM in 1954 decided that an international system should be derived from six base units to replace many traditional [[Systems of measurement|measurement systems]]. At provide for the end of World War II, a number measurement of different systems of measurement were still temperature and optical radiation in use throughout the worldaddition to mechanical and electromagnetic quantities. Some of these systems The six base units that were metric<!-system variations, whereas others were based on customary systems. It was recognised -"that additional steps were needed to [[metrication|promote a worldwide measurement system]]. As a result, " expresses the 9th General Conference on Weights preterit, and Measures the following predicate "are" connotes the non-changing entity no matter where in time of the complements "metre," "kilogram," "second," "ampere," "kelvin," "candela"-->recommended are the metre, kilogram, second, ampere, degree Kelvin ([[CGPM]]later renamed kelvin), in 1948and candela. In 1960, asked the 11th CGPM named the system the ''International Committee for Weights and Measures ([[CIPM]]) to conduct an international study System of Units. The seventh base unit, the measurement needs of the scientificmole mole, technical, and educational communitieswas added in 1971 by the 14th CGPM.

Based on the findings of this study, the 10th CGPM in 1954 decided that an international system should be derived from six base units to provide for the measurement of temperature and optical radiation in addition to mechanical and [[SI electromagnetism units|electromagnetic]] quantities. The six base units that were <!--"that were" expresses the preterit, and the following predicate "are" connotes the non-changing entity no matter where in time of the complements "metre," "kilogram," "second," "ampere," "kelvin," "candela"-->recommended are the [[metre]], [[kilogram]], [[second]], [[ampere]], degree Kelvin (later renamed [[kelvin]]), and [[candela]]. In 1960, the 11th CGPM named the system the ''International System of Units'', abbreviated SI from the French name, {{lang|fr|''Le Système international d'unités''}}. The seventh base unit, the [[mole (unit)|mole]], was added in 1971 by the 14th CGPM. One of the CIPM committees, the CCU, has proposed a number of [[new SI definitions|changes]] to the definitions of the base units used in SI.

The International System of Units consists of a set of units together with a set of SI. The units are divided into two classes&mdash;'''base units''' and '''derived units'''. There are seven SI, each representing, by convention, [[Dimensional analysis|different kinds of physical quantities]].

![[Dimensional analysis|Dimension symbol]]

![[metre]]

|[[length]]

![[kilogram]]