Outline of the metric system explained

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:

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.

Unit name	Quantity			Other metric	Non-metric
abampere			Derived metric unit with a special name
abcoulomb			Derived metric unit with a special name
abhenry			Derived metric unit with a special name
abohm			Derived metric unit with a special name
abvolt			Derived metric unit with a special name
ampere		Base unit
ampere-meter		Derived coherent SI unit without a special name
apostilb			Derived metric unit with a special name
astronomical unit		Non-SI unit permitted for use with SI units
dalton		Non-SI unit permitted for use with SI units
barye			Derived metric unit with a special name
becquerel		Derived SI unit with a special name
bril					No specified relationship
candela		Base unit
candela per square metre		Derived coherent SI unit without a special name
centimetre		Multiple or submultiple of an SI base unit	Base unit
coulomb		Derived SI unit with a special name
cubic centimetre		Derived coherent SI unit without a special name	Derived coherent metric unit without a special name
cubic metre		Derived coherent SI unit without a special name	Derived coherent metric unit without a special name
cubic metre per second		Derived coherent SI unit without a special name	Derived coherent metric unit without a special name
curie			Derived metric unit with a special name
day		Non-SI unit permitted for use with SI units
decibel		Non-SI unit permitted for use with SI units
degree Celsius		Derived SI unit with a special name
degree of arc		Non-SI unit permitted for use with SI units
dyne			Derived metric unit with a special name
electronvolt		Non-SI unit permitted for use with SI units
erg			Derived metric unit with a special name
farad		Derived SI unit with a special name
gal			Derived SI unit with a special name
gauss			Derived metric unit with a special name
gram		Multiple or submultiple of an SI base unit	Base unit
grave				Base unit
gray		Derived SI unit with a special name
hectare		Non-SI unit permitted for use with SI units		Multiple or submultiple of a base unit
henry		Derived SI unit with a special name
hertz		Derived SI unit with a special name	Derived metric unit with a special name
hour		Non-SI unit permitted for use with SI units			No specified relationship
joule		Derived SI unit with a special name
joule per mole		Derived coherent SI unit without a special name
joule-second		Derived coherent SI unit without a special name
katal		Derived SI unit with a special name
kelvin		Base unit	Base unit
kilogram		Base unit	Multiple or submultiple of a base unit
kilogram per cubic metre		Derived coherent SI unit without a special name	Derived coherent metric unit without a special name
kilometre per hour					No specified relationship
litre		Non-SI unit permitted for use with SI units
lumen		Derived SI unit with a special name
lumen second		Derived coherent SI unit without a special name
lux		Derived SI unit with a special name
lux second		Derived coherent SI unit without a special name
maxwell			Derived metric unit with a special name
metre per second squared		Derived coherent SI unit without a special name	Derived coherent metric unit without a special name
metre squared per second		Derived coherent SI unit without a special name	Derived coherent metric unit without a special name
metre		Base unit	Multiple or submultiple of a base unit
microgram		Multiple or submultiple of an SI base unit	Multiple or submultiple of a base unit
minute		Non-SI unit permitted for use with SI units			No specified relationship
minute of arc		Non-SI unit permitted for use with SI units
mole		Base unit
neper		Non-SI unit permitted for use with SI units
newton		Derived SI unit with a special name
newton-metre		Derived SI metric unit without a special name
newton-second		Derived coherent SI unit without a special name
oersted			Derived SI unit with a special name
ohm		Derived SI unit with a special name
pascal		Derived SI unit with a special name
phot			Derived coherent metric unit without a special name
poise			Derived metric unit with a special name
radian		Derived coherent SI unit with a special name
radian per second		Derived coherent SI unit without a special name
rayleigh				No specified relationship
	kerma of X-rays and gamma rays		Derived coherent metric unit without a special name
roentgen equivalent man			Derived coherent metric unit without a special name
second		Base unit	Base unit
siemens		Derived SI unit with a special name
sievert		Derived SI unit with a special name
skot				No specified relationship
square kilometre		Derived SI unit without a special name	Derived coherent metric unit without a special name
square metre		Derived coherent SI unit without a special name	Derived coherent metric unit without a special name
statcoulomb			Derived metric unit with a special name
statvolt			Derived metric unit with a special name
steradian		Derived coherent SI unit with a special name
stilb			Derived coherent metric unit without a special name
stokes			Derived metric unit with a special name
tesla		Derived SI unit with a special name
tonne		Non-SI unit permitted for use with SI units
torr				No specified relationship
volt		Derived SI unit with a special name
watt		Derived SI unit with a special name
watt-second		Derived coherent SI unit without a special name
weber		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.

Future of the metric system

2019 redefinition of the SI base units - changes in the definitions of the International System of Units, which are based on defined values of physical constants, in use since May 2019.

Metrication groups and authorities

US Metric Association (USA, 1916–current)
Metric Commission (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 text (Thomas Jefferson 1790)

Persons influential in the metric system

Simon Stevin (1548–1620)
Gabriel Mouton (1618–1694)
Marquis de Condorcet (1743–1794)
Pierre Méchain (1744–1804)
Pierre-Simon Laplace (1749–1827)
Jean Baptiste Joseph Delambre (1749–1822)
Adrien-Marie Legendre (1753–1834)
James Clerk Maxwell (1831–1879)
William Thomson, 1st Baron Kelvin (1824–1907)
Giovanni Giorgi (1871–1950)

External links

Metric conversions