The following outline is provided as an overview of and topical guide to the

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 ...

– various loosely related

systems of measurement A 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. Systems of measurement i ...

that trace their origin to the decimal system of measurement introduced in France during the

French Revolution The French Revolution ( ) was a period of radical political and societal change in France that began with the Estates General of 1789 and ended with the formation of the French Consulate in November 1799. Many of its ideas are conside ...

Nature of the metric system

The metric system can be described as all of the following: *

System A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundaries, structure and purpose and express ...

– set of interacting or interdependent components forming an integrated whole. **

System of measurement A 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. Systems of measurement i ...

– set of units which can be used to specify anything which can be measured. Historically, systems of measurement were initially defined and regulated to support trade and internal commerce. Units were arbitrarily defined by fiat (see statutory law) by the ruling entities and were not necessarily well inter-related or self-consistent. When later analyzed and scientifically, some quantities were designated as base units, meaning all other needed units of measure could be derived from them.

Essence of the metric system

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. ...

(SI) is the system of units that has been officially endorsed under the

Metre Convention The Metre Convention (french: link=no, Convention du Mètre), also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Braz ...

since 1960. Child articles are: :*

SI base unit The SI base units are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities: they are notably a basic set from which al ...

SI derived unit SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI). They can be expressed as a product (or ratio) of one or more of the base units, possibly scaled by an appropriate p ...

Non-SI units mentioned in the SI This is a list of units that are not defined as part of the International System of Units (SI) but are otherwise mentioned in the SI Brochure, Bureau international des poids et mesures, "Non-SI units that are accepted for use with the SI", inLe Sy ...

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 ...

Underlying philosophy

Discussions of the underlying philosophy of the metric system (and other systems of measure) include: *

Coherence (units of measurement) A coherent system of units is a system of units of measurement used to express physical quantities that are defined in such a way that the equations relating the numerical values expressed in the units of the system have exactly the same form, inc ...

* Realisation (metrology)

Metric units of measure

Articles that exist for many units of measure that are related to various flavours of the metric system are catalogued below.

History of the metric system

History of the metric system The history of the metric system began during the Age of Enlightenment with measures of length and weight derived from nature, along with their decimal multiples and fractions. The system became the standard of France and Europe within half ...

– the metric system developed from a decimal system of measurement adopted by France after the French Revolution.

Chronological history of the metric system

Principal dates in the development of the metric system include: *1792 – Initiation of a decimal system of measurement by the French Revolutionary Government *1799 – The ''Metre des archives'' and ''kilogram des archives'' become the standards for the

. *1861 – Concept of unit coherence introduced by Maxwell – the base units were the

centimetre 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter. A centimetre (international spelling) or centimeter (American spellin ...

gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...

and

second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ea ...

. *1875 – Under the

Convention of the metre The Metre Convention (french: link=no, Convention du Mètre), also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Braz ...

, a new body the

General Conference on Weights and Measures The General Conference on Weights and Measures (GCWM; french: Conférence générale des poids et mesures, CGPM) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established i ...

(CGPM) was set up and given responsibility for the new international prototype of the kilogram and international prototype of the metre which replaced the old French copies as the definitive prototypes of the metre and the kilogram. *1881 – International Electric Congress agrees on standards for electrical units (formalised in 1893) *1921 – Convention of the metre extended to cover all physical units of measure *1960 – The CGPM published the metric system under the name "

" (SI) a coherent system of units based on the kilogram, metre, second,

ampere The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...

and

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and ...

History of metrication

History of

metrication 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 ...

– metrication is the process by which legacy, national-specific systems of measurement were replaced by the metric system. *

Metrication in Australia Metrication in Australia effectively began in 1966 with the conversion to decimal currency under the auspices of the Decimal Currency Board. The conversion of measurements—metrication—commenced subsequently in 1971, under the direction of ...

* Metrication in Barbados *

Metrication in Canada Metrication in Canada began in 1970 and ceased in 1985. While Canada has converted to the metric system for many purposes, there is still significant use of non-metric units and standards in many sectors of the Canadian economy and everyday life t ...

* Metrication in Chile *

Metrication in Guatemala In Guatemala the metric system is official but it uses a mixture of U.S., metric and Spanish customary units. History In May 1910 most of Central America adopted a common system of measurements.Ministerio de Economía de GuatemalaSistema Internaci ...

* Metrication in Hong Kong *

Metrication in India 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 1 ...

* Metrication in Ireland * Metrication in Jamaica *

Metrication in New Zealand New Zealand started metrication in 1969 with the establishment of the Metric Advisory Board (MAB) and completed metrication on 14 December 1976. Until the 1970s, New Zealand traditionally used the imperial system for measurement, which it had inh ...

* Metrication in Peru * Metrication in Sweden *

Metrication in the United Kingdom Metrication, the process of introducing the metric system of measurement in place of imperial units, has made steady progress in the United Kingdom since the mid-20th century but today remains equivocal and varies by context. Most of government, ...

** British Metrication Board *

Metrication in the United States Metrication (or metrification) 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 ...

** Plan for Establishing Uniformity in the USA,

Thomas Jefferson Thomas Jefferson (April 13, 1743 – July 4, 1826) was an American statesman, diplomat, lawyer, architect, philosopher, and Founding Fathers of the United States, Founding Father who served as the third president of the United States from 18 ...

's report (1790) which included a proposal for decimal system based on a "decimal foot" **

United States Metric Board The United States Metric Board (USMB) was a United States government agency set up to encourage metrication. The United States Metric Board was commissioned by the Metric Conversion Act of 1975 (15 U.S.C. 205d, enacted on December 23, 1975). The ...

Historical metric system variants

Four variants of the metric system that predate the introduction of SI (1960) are described in varying levels of detail: *

MKS system of units The MKS system of units is a physical system of measurement that uses the metre, kilogram, and second (MKS) as base units. It forms the base of the International System of Units (SI), though SI has since been redefined by different fundament ...

formed the basis for SI. *

Centimetre–gram–second system of units The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units ...

was the principal variant of the metric system that evolved in stages until it was superseded by SI. *

Gravitational metric system The gravitational metric system (original French term ) is a non-standard system of units, which does not comply with the International System of Units (SI). It is built on the three base quantities length, time and force with base units metr ...

was a little-used variant of the metric system that normalised the acceleration due to gravity. *

Metre–tonne–second system of units The metre–tonne–second or MTS system of units is a system of physical units. It was invented in France, hence the unit names ''sthène'' and ''pièze'', and became its legal system between 1919 and 1961 ("décret" 5 May 1961, "Journal Officie ...

was a variant of the metric system used in French and Russian industry between the First and

Second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ea ...

World Wars. Between 1812 and 1839 France used a quasi-metric system: *

Mesures usuelles Mesures usuelles (, ''customary measurements'') were a French system of measurement introduced by Napoleon I in 1812 to act as compromise between the metric system and traditional measurements. The system was restricted to use in the retail indu ...

History of metric units

History of the metre The history of the metre starts with the Scientific Revolution that is considered to have begun with Nicolaus Copernicus's publication of ''De revolutionibus orbium coelestium'' in 1543. Increasingly accurate measurements were required, and s ...

Politics of the metric system

Prior to 1875 the metric system was controlled by the French Government. In that year, seventeen nations signed the

and the management and administration of the system passed into international control. *

describes the 1875 treaty and its development to the modern day. Three organisations, the CGPM, CIPM and BIPM were set up under the convention. *

(''Conférence générale des poids et mesures'' or CGPM) – a meeting every four to six years of delegates from all member states. *The

International Committee for Weights and Measures The General Conference on Weights and Measures (GCWM; french: Conférence générale des poids et mesures, CGPM) is the supreme authority of the International Bureau of Weights and Measures (BIPM), the intergovernmental organization established i ...

(''Comité international des poids et mesures'' or CIPM) – an advisory body to the CGPM consisting of prominent metrologists. *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 ...

(''Bureau international des poids et mesures'' or BIPM) – an organisation based at Sèvres, France that has custody of the

international prototype of the kilogram The International Prototype of the Kilogram (referred to by metrology, metrologists as the IPK or Le Grand K; sometimes called the ''wiktionary:ur-#Prefix, ur-kilogram,'' or ''urkilogram,'' particularly by German-language authors writing in Engli ...

, provides

metrology Metrology is the scientific study of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in Fran ...

services for the CGPM and CIPM, houses the secretariat for these organisations and hosts their formal meetings. Both the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...

and the

International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in A ...

have issued directives/recommendations to harmonise the use of units of measure. These documents endorse the use of SI for most purposes. * European units of measurement directives * ISO/IEC 80000

Future of the metric system

2019 redefinition of the SI base units In 2019, four of the seven SI base units specified in the International System of Quantities were redefined in terms of natural physical constants, rather than human artifacts such as the standard kilogram. Effective 20 May 2019, the 144th ...

– changes in the definitions of the

, which are based on defined values of physical constants, in use since May 2019.

Metrication groups and authorities

US Metric Association The US Metric Association (USMA), based in Windsor, Colorado, is a non-profit organization that advocates for total conversion of the United States to the International System of Units (SI). Founded on 27 December 1916 at Columbia University i ...

(USA, 1916–current) *

Metric Commission The Metric Commission (french: Commission du système métrique), formally the Preparatory Commission for the Conversion to the Metric System, was a Canadian government agency established by the federal government in 1971 to facilitate Canada's co ...

(Canada, 1971–1985) * Metrication Board (United Kingdom, 1969–1981)

Metric system publications

*''

Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States The "Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States" was a report submitted to the U.S. House of Representatives on July 13, 1790, by Secretary of State Thomas Jefferson. At the First United States Cong ...

'
text
(

1790)

Persons influential in the metric system

Simon Stevin Simon Stevin (; 1548–1620), sometimes called Stevinus, was a Flemish mathematician, scientist and music theorist. He made various contributions in many areas of science and engineering, both theoretical and practical. He also translated vario ...

(1548–1620) * Gabriel Mouton (1618–1694) *

Marquis de Condorcet Marie Jean Antoine Nicolas de Caritat, Marquis of Condorcet (; 17 September 1743 – 29 March 1794), known as Nicolas de Condorcet, was a French philosopher and mathematician. His ideas, including support for a liberal economy, free and equal pu ...

(1743–1794) *

Pierre Méchain Pierre François André Méchain (; 16 August 1744 – 20 September 1804) was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep-sky objects and comets. Life Pierre Méchain was born i ...

(1744–1804) *

Pierre-Simon Laplace Pierre-Simon, marquis de Laplace (; ; 23 March 1749 – 5 March 1827) was a French scholar and polymath whose work was important to the development of engineering, mathematics, statistics, physics, astronomy, and philosophy. He summarize ...

(1749–1827) *

Jean Baptiste Joseph Delambre Jean Baptiste Joseph, chevalier Delambre (19 September 1749 – 19 August 1822) was a French mathematician, astronomer, historian of astronomy, and geodesist. He was also director of the Paris Observatory, and author of well-known books on t ...

(1749–1822) *

Adrien-Marie Legendre Adrien-Marie Legendre (; ; 18 September 1752 – 9 January 1833) was a French mathematician who made numerous contributions to mathematics. Well-known and important concepts such as the Legendre polynomials and Legendre transformation are name ...

(1753–1834) *

James Clerk Maxwell James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and scientist responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and ligh ...

(1831–1879) *

William Thomson, 1st Baron Kelvin William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, Mathematical physics, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy (Glasgow), Professor of Natural Philoso ...

(1824–1907) *

Giovanni Giorgi Giovanni Giorgi (November 27, 1871 – August 19, 1950) was an Italian physicist and electrical engineer who proposed the ''Giorgi system'' of measurement, the precursor to the International System of Units (SI). Early Life Giovanni Giorgi was b ...

(1871–1950)

References

External links

Metric conversions
{{Systems of measurement *Outline

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 ...