TheInfoList

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 fundamental 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. The codes in the various columns have the following meanings:

• A – Base unit
• B – Multiple or submultiple of a base unit
• C – Derived metric unit with a special name
• D – Derived coherent metric unit that has no special name
• E – Non-coherent unit explicitly permitted for use within the metric system (SI only)
• F – Unit of measure that has an association with the metric system
• X – No specified relationship (Other metric only)
Name Quantity SI unit cgs unit Other metric Non-metric
abampere electric current C
abcoulomb electric charge C
abhenry inductance C
abohm electrical resistance C
abvolt potential difference C
ampere electric current A
ampere-meter magnetic pole strength D
apostilb luminance C
astronomical unit length E
dalton mass E
barye pressure C
bril luminance X
candela per square metre luminance D
candela luminous intensity A
degree Celsius temperature C
centimetre length B A
coulomb electric charge C
cubic centimetre volume D D
cubic metre per second volumetric flow rate D D
cubic metre volume D D
day time E
decibel level E
degree of arc angle E
dyne force C
electronvolt energy E
erg energy C
gal acceleration C
gauss magnetic flux density C
gram mass B A
grave mass A
gray absorbed dose C
hectare area E B
henry inductance C
hertz frequency C C
hour time E X
joule per mole energy per amount of substance D
joule energy C
joule-second angular momentum D
katal catalytic activity C
kelvin temperature A A
kilogram per cubic metre density D D
kilogram mass A B
kilometres per hour velocity X
litre volume E
lumen luminous flux C
lumen second luminous energy D
lux second luminous exposure D
lux illuminance C
maxwell magnetic flux C
metre per second squared acceleration D D
metre squared per second angular momentum D D
metre length A B
microgram mass B B
minute of arc angle E
minute time E X
mole amount of substance A
neper level E
newton force C
newton metre torque D
newton-second impulse or momentum D
oersted magnetic field strength C
ohm electric resistance C
pascal pressure C
phot illuminance D
poise dynamic viscosity C
radian per second angular frequency D
rayleigh photon flux X
roentgen kerma of X-rays and gamma rays D
roentgen equivalent man radiation dose equivalent D
second time A A
siemens electric conductance C
skot luminance X
square kilometre area D D
square metre area D D
statcoulomb electric charge C
statvolt potential difference C
stilb luminance D
torr pressure X
stokes kinematic viscosity C
tesla magnetic field strength C
tonne mass E
volt potential difference C
watt second energy D
watt power C
weber magnetic flux C

## 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 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.