The following outline is provided as an overview of and topical guide to the metric system:
Metric system – various loosely related systems of measurement that trace their origin to the decimal system of measurement introduced in France during the French Revolution.
Nature of the metric system
The metric system can be described as all of the following:
System – set of interacting or interdependent components forming an integrated whole. System of measurement – 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 (SI) is the system of units that has been officially endorsed under the Metre Convention since 1960. Child articles are: SI base unit SI derived unit Non-SI units mentioned in the SI Metric prefixes
Underlying philosophy Discussions of the underlying philosophy of the metric system (and other systems of measure) include: Coherence (units of measurement) Realisation (metrology)
Metric units of measure Articles that exist for many metric units of measure are catalogued below.
Unit name Quantity SI unit cgs unit Other metric Non-metric abampere electric current Derived metric unit with a special name abcoulomb electric charge Derived metric unit with a special name abhenry inductance Derived metric unit with a special name abohm electrical resistance Derived metric unit with a special name abvolt potential difference Derived metric unit with a special name ampereelectric current Base unit ampere-meter magnetic pole strength Derived coherent SI unit without a special name apostilb luminance Derived metric unit with a special name astronomical unit length Non-SI unit permitted for use with SI units dalton mass Non-SI unit permitted for use with SI units barye pressure Derived metric unit with a special name becquerel radioactive activity Derived SI unit with a special name bril luminance No specified relationship candela luminous intensity Base unit candela per square metre luminance Derived coherent SI unit without a special name centimetre length Multiple or submultiple of an SI base unit Base unit coulomb electric charge Derived SI unit with a special name cubic centimetre volume Derived coherent SI unit without a special name Derived coherent metric unit without a special name cubic metre volume Derived coherent SI unit without a special name Derived coherent metric unit without a special name cubic metre per second volumetric flow rate Derived coherent SI unit without a special name Derived coherent metric unit without a special name curie radioactive activity Derived metric unit with a special name day time Non-SI unit permitted for use with SI units decibel level Non-SI unit permitted for use with SI units degree Celsius temperature Derived SI unit with a special name degree of arc angle Non-SI unit permitted for use with SI units dyne force Derived metric unit with a special name electronvolt energy Non-SI unit permitted for use with SI units erg energy Derived metric unit with a special name farad capacitance Derived SI unit with a special name gal acceleration Derived SI unit with a special name gauss magnetic flux density Derived metric unit with a special name gram mass Multiple or submultiple of an SI base unit Base unit grave mass Base unit gray absorbed dose Derived SI unit with a special name hectare area Non-SI unit permitted for use with SI units Multiple or submultiple of a base unit henry inductance Derived SI unit with a special name hertz frequency Derived SI unit with a special name Derived metric unit with a special name hour time Non-SI unit permitted for use with SI units No specified relationship joule energy Derived SI unit with a special name joule per mole energy per amount of substance Derived coherent SI unit without a special name joule-second angular momentum Derived coherent SI unit without a special name katal catalytic activity Derived SI unit with a special name kelvin temperature Base unit Base unit kilogram mass Base unit Multiple or submultiple of a base unit kilogram per cubic metre density Derived coherent SI unit without a special name Derived coherent metric unit without a special name kilometre per hour velocity No specified relationship litre volume Non-SI unit permitted for use with SI units Multiple or submultiple of a base unit lumen luminous flux Derived SI unit with a special name lumen second luminous energy Derived coherent SI unit without a special name lux illuminance Derived SI unit with a special name lux second luminous exposure Derived coherent SI unit without a special name maxwell magnetic flux Derived metric unit with a special name metre per second squared acceleration Derived coherent SI unit without a special name Derived coherent metric unit without a special name metre squared per second angular momentum Derived coherent SI unit without a special name Derived coherent metric unit without a special name metre length Base unit Multiple or submultiple of a base unit microgram mass Multiple or submultiple of an SI base unit Multiple or submultiple of a base unit minute time Non-SI unit permitted for use with SI units No specified relationship minute of arc angle Non-SI unit permitted for use with SI units mole amount of substance Base unit neper level Non-SI unit permitted for use with SI units newton force Derived SI unit with a special name newton-metre torque Derived SI metric unit without a special name newton-second impulse or momentum Derived coherent SI unit without a special name oersted magnetic field strength Derived SI unit with a special name ohm electric resistance Derived SI unit with a special name pascal pressure Derived SI unit with a special name phot illuminance Derived coherent metric unit without a special name poise dynamic viscosity Derived metric unit with a special name radian angle Derived coherent SI unit with a special name radian per second angular frequency Derived coherent SI unit without a special name rayleigh photon flux No specified relationship roentgen kerma of X-rays and gamma rays Derived coherent metric unit without a special name roentgen equivalent man radiation dose equivalent Derived coherent metric unit without a special name second time Base unit Base unit siemens electric conductance Derived SI unit with a special name sievert radiation dose equivalent Derived SI unit with a special name skot luminance No specified relationship square kilometre area Derived SI unit without a special name Derived coherent metric unit without a special name square metre area Derived coherent SI unit without a special name Derived coherent metric unit without a special name statcoulomb electric charge Derived metric unit with a special name statvolt potential difference Derived metric unit with a special name steradian solid angle Derived coherent SI unit with a special name stilb luminance Derived coherent metric unit without a special name stokes kinematic viscosity Derived metric unit with a special name tesla magnetic field strength Derived SI unit with a special name tonne mass Non-SI unit permitted for use with SI units Multiple or submultiple of a base unit torr pressure No specified relationship volt potential difference Derived SI unit with a special name watt power Derived SI unit with a special name watt-second energy Derived coherent SI unit without a special name weber magnetic flux Derived SI unit with a special name
History of the metric system
History of the metric system – 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 metric system. 1861 – Concept of unit coherence introduced by Maxwell – the base units were the centimetre, gram and second. 1875 – Under the Convention of the metre, a new body the General Conference on Weights and Measures (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 "International System of Units" (SI) a coherent system of units based on the kilogram, metre, second, ampere and kelvin.
History of metrication
History of metrication – metrication is the process by which legacy, national-specific systems of measurement were replaced by the metric system. Metrication in Australia Metrication in Barbados Metrication in Canada Metrication in Chile Metrication in Guatemala Metrication in Hong Kong Metrication in India Metrication in Ireland Metrication in Jamaica Metrication in New Zealand Metrication in Peru Metrication in Sweden Metrication in the United Kingdom British Metrication Board Metrication in the United States Plan for Establishing Uniformity in the USA, Thomas Jefferson's report (1790) which included a proposal for decimal system based on a "decimal foot" United States Metric Board
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 formed the basis for SI. Centimetre–gram–second system of units was the principal variant of the metric system that evolved in stages until it was superseded by SI. Gravitational metric system was a little-used variant of the metric system that normalised the acceleration due to gravity. Metre–tonne–second system of units was a variant of the metric system used in French and Russian industry between the First and Second World Wars.
Between 1812 and 1839 France used a quasi-metric system: Mesures usuelles
History of metric units History of the metre
Politics of the metric system Prior to 1875 the metric system was controlled by the French Government. In that year, seventeen nations signed the Metre Convention and the management and administration of the system passed into international control. Metre Convention describes the 1875 treaty and its development to the modern day. Three organisations, the CGPM, CIPM and BIPM were set up under the convention. 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. The International Committee for Weights and Measures (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 (Bureau international des poids et mesures or BIPM) – an organisation based at Sèvres, France that has custody of the international prototype of the kilogram, provides metrology services for the CGPM and CIPM, houses the secretariat for these organisations and hosts their formal meetings.
Both the European Union and the International Organization for Standardization have issued directives/recommendations to harmonise the use of units of measure. These documents endorse the use of SI for most purposes.