## International System of Units |

the

**international system of units**(**si**, abbreviated from thefrench ) is the modern form of the*système international (d'unités)* and is the most widely usedmetric system . it comprises asystem of measurement system ofcoherent built on sevenunits of measurement , which are thebase units ,second ,metre ,kilogram ,ampere ,kelvin ,mole , and a set of twentycandela to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. the system also gives names to 22prefixes , such asderived units andlumen , for other common physical quantities.watt the si is based on a system of base

–quantities ,time ,length ,mass ,electric current ,thermodynamic temperature , andamount of substance – and their relationships, now a subset of theluminous intensity . theinternational system of quantities have been defined in terms ofsi base units , such as theinvariant constants of nature in vacuum and thespeed of light , which can be observed and measured with great accuracy. seven constants are used in various combinations to define the seven base units. prior to 2019, artefacts were used instead of some of these constants, the last being thecharge of the electron , a cylinder ofinternational prototype of the kilogram . concern regarding its stability led to aplatinum-iridium entirely in terms of constants of nature, which was put into effect on 20 may 2019.revision of the definition of the base units ^{[1]} may be defined in terms of base units or other derived units. they are adopted to facilitate measurement of diverse quantities. the si is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology ofderived units progresses and the precision of measurements improves. the most recently named derived unit, themeasurement , was defined in 1999.katal the reliability of the si depends not only on the precise measurement of standards for the base units in terms of various

of nature, but also on precise definition of those constants. the set of underlying constants is modified as more stable constants are found, or may be more precisely measured. for example, in 1983 the metre was redefined as the distance that light propagates inphysical constants in a given fraction of a second, thus making the value of thevacuum in terms of the defined units exact.speed of light the motivation for the development of the si was the diversity of units that had sprung up within the

(cgs) systems (specifically the inconsistency between the systems ofcentimetre–gram–second andelectrostatic units ) and the lack of coordination between the variouselectromagnetic units that used them. thedisciplines (french:general conference on weights and measures – cgpm), which was established by the*conférence générale des poids et mesures* of 1875, brought together many international organisations to establish the definitions and standards of a new system and to standardise the rules for writing and presenting measurements. the system was published in 1960 as a result of an initiative that began in 1948. it is based on themetre convention (mks) rather than any variant of the cgs.metre–kilogram–second system of units - units and prefixes
- lexicographic conventions
- international system of quantities
- realisation of units
- evolution of the si
- history
- see also
- notes
- references
- further reading
- external links

The **International System of Units** (**SI**, abbreviated from the * Système international (d'unités)*) is the modern form of the

The SI is based on a system of base ^{[1]}

The reliability of the SI depends not only on the precise measurement of standards for the base units in terms of various

The motivation for the development of the SI was the diversity of units that had sprung up within the * Conférence générale des poids et mesures* – CGPM), which was established by the