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Metric Units

S.I. Base Units

The International System of Units (S.I.) defines seven base units for the seven base quantities:

Quantity    Name    Symbol
lengthmeter (or metre)m
electric currentampereA
thermodynamic temperaturekelvinK
luminous intensitycandelacd
amount of substancemolemol

S.I. Derived Units

Derived units are defined in terms of the seven base units.

area          square meter          m2

S.I. Derived Units with Special Names

Quantity   Name    Symbol    Derivation
force newtonNkg m s-2
pascalPaN m-2
quantity of heat
jouleJN m
powerwattWJ s-1
electric chargecoulombCA s
potential differencevoltVW A-1
electromotive forcevoltVJ C-1
capacitancefaradFC V-1
resistanceohmomegaV A-1
magnetic fluxweberWbV s
magnetic flux density,
magnetic induction
teslaTWb m-2
inductancehenryHV s A-1
luminous fluxlumenlmcd sr
illuminationluxlxlm m-2

S.I. Supplementary Units

Quantity    Name    Symbol    Derivation
areahectareha104 m2
volumeliter (or litre)l10-3 m3
plane angleradianrad
solid anglesteradiansr

S.I. Prefixes for Multiples and Submultiples

The International System of Units (S.I.) defines 20 prefixes used to form decimal multipliers for the S.I. units:

PrefixSymbolMeaning PrefixSymbolMeaning
yottaY1024 millim10-3
zettaZ1021 microµ10-6
exaE1018 nanon10-9
petaP1015 picop10-12
teraT1012 femtof10-15
gigaG109 attoa10-18
megaM106 zeptoz10-21
kilok103 yoctoy10-24
hectoh102 decid10-1
decada10 centic10-2

cm = 10-2 m   = 0.01 m
km = 103 m    = 1000 m


The kilogram is the only S.I. base unit that already includes a prefix.
Therefore 1 gram (g) = 0.001 kilogram (kg).