# Outline of the metric system

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

### 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.

NameQuantitySI unitcgs unitOther metricNon-metric
abampere electric currentDerived metric unit with a special name
abcoulomb electric chargeDerived metric unit with a special name
abhenry inductanceDerived metric unit with a special name
abohm electrical resistanceDerived metric unit with a special name
abvolt potential differenceDerived metric unit with a special name
ampere electric currentBase unit
ampere-meter magnetic pole strengthDerived coherent metric unit that has no special name
apostilb luminanceDerived metric unit with a special name
astronomical unit lengthNon-coherent unit explicitly permitted for use within the metric system
dalton massNon-coherent unit explicitly permitted for use within the metric system
barye pressureDerived metric unit with a special name
becquerel radioactive activityDerived metric unit with a special name
bril luminanceNo specified relationship
candela per square metre luminanceDerived coherent metric unit that has no special name
candela luminous intensityBase unit
degree Celsius temperatureDerived metric unit with a special name
centimetre lengthMultiple or submultiple of a base unitBase unit
coulomb electric chargeDerived metric unit with a special name
cubic centimetre volumeDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
cubic metre per second volumetric flow rateDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
cubic metre volumeDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
curie radioactive activityDerived metric unit with a special name
day timeNon-coherent unit explicitly permitted for use within the metric system
decibel levelNon-coherent unit explicitly permitted for use within the metric system
degree of arc angleNon-coherent unit explicitly permitted for use within the metric system
dyne forceDerived metric unit with a special name
electronvolt energyNon-coherent unit explicitly permitted for use within the metric system
erg energyDerived metric unit with a special name
farad capacitanceDerived metric unit with a special name
gal accelerationDerived metric unit with a special name
gauss magnetic flux densityDerived metric unit with a special name
gram massMultiple or submultiple of a base unitBase unit
grave massBase unit
gray absorbed doseDerived metric unit with a special name
hectare areaNon-coherent unit explicitly permitted for use within the metric systemMultiple or submultiple of a base unit
henry inductanceDerived metric unit with a special name
hertz frequencyDerived metric unit with a special nameDerived metric unit with a special name
hour timeNon-coherent unit explicitly permitted for use within the metric systemNo specified relationship
joule per mole energy per amount of substanceDerived coherent metric unit that has no special name
joule energyDerived metric unit with a special name
joule-second angular momentumDerived coherent metric unit that has no special name
katal catalytic activityDerived metric unit with a special name
kelvin temperatureBase unitBase unit
kilogram per cubic metre densityDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
kilogram massBase unitMultiple or submultiple of a base unit
kilometres per hour velocityNo specified relationship
litre volumeNon-coherent unit explicitly permitted for use within the metric system
lumen luminous fluxDerived metric unit with a special name
lumen second luminous energyDerived coherent metric unit that has no special name
lux second luminous exposureDerived coherent metric unit that has no special name
lux illuminanceDerived metric unit with a special name
maxwell magnetic fluxDerived metric unit with a special name
metre per second squared accelerationDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
metre squared per second angular momentumDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
metre lengthBase unitMultiple or submultiple of a base unit
microgram massMultiple or submultiple of a base unitMultiple or submultiple of a base unit
minute of arc angleNon-coherent unit explicitly permitted for use within the metric system
minute timeNon-coherent unit explicitly permitted for use within the metric systemNo specified relationship
mole amount of substanceBase unit
neper levelNon-coherent unit explicitly permitted for use within the metric system
newton forceDerived metric unit with a special name
newton metre torqueDerived coherent metric unit that has no special name
newton-second impulse or momentumDerived coherent metric unit that has no special name
oersted magnetic field strengthDerived metric unit with a special name
ohm electric resistanceDerived metric unit with a special name
pascal pressureDerived metric unit with a special name
phot illuminanceDerived coherent metric unit that has no special name
poise dynamic viscosityDerived metric unit with a special name
radian per second angular frequencyDerived coherent metric unit that has no special name
radian angleDerived metric unit with a special name
rayleigh photon fluxNo specified relationship
roentgen kerma of X-rays and gamma raysDerived coherent metric unit that has no special name
roentgen equivalent man radiation dose equivalentDerived coherent metric unit that has no special name
second timeBase unitBase unit
siemens electric conductanceDerived metric unit with a special name
sievert radiation dose equivalentDerived metric unit with a special name
skot luminanceNo specified relationship
square kilometre areaDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
square metre areaDerived coherent metric unit that has no special nameDerived coherent metric unit that has no special name
statcoulomb electric chargeDerived metric unit with a special name
statvolt potential differenceDerived metric unit with a special name
steradian solid angleDerived metric unit with a special name
stilb luminanceDerived coherent metric unit that has no special name
torr pressureNo specified relationship
stokes kinematic viscosityDerived metric unit with a special name
tesla magnetic field strengthDerived metric unit with a special name
tonne massNon-coherent unit explicitly permitted for use within the metric system
volt potential differenceDerived metric unit with a special name
watt second energyDerived coherent metric unit that has no special name
watt powerDerived metric unit with a special name
weber magnetic fluxDerived metric 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:[1]

• 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 kilogram and international prototype metre which replaced the old French copies as the definitive prototype metre and 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.

### Historical metric system variants

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

Between 1812 and 1839 France used a quasi-metric system:

## 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.

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.