International System of Units

A to Z Drug Facts

International System of Units

The Système international d 'unités (International System of Units) or SI is a modernized version of the metric system. The primary goal of the conversion to SI units is to revise the present confused measurement system and to improve test-result communications.

The SI has 7 basic units from which other units are derived:

Base Units of SI
Physical quantity Base unit SI symbol
length meter m
mass kilogram kg
time second s
amount of substance mole mol
thermodynamic temperature kelvin K
electric current ampere A
luminous intensity candela cd

Combinations of these base units can express any property, although, for simplicity, special names are given to some of these derived units.

Representative Derived Units
Derived unit Name and symbol Derivation from base units
area square meter m2
volume cubic meter m3
force newton (N) kg•m•s –2
pressure pascal (Pa) kg•m –1 •s-2 (N/m2)
work, energy joule (J) kg•m2 •s –2 (N•m)
mass density kilogram per cubic meter kg/m3
frequency hertz (Hz) 1 cycles/s–1
temperature degree concentration Celsius (°C) °C = °K –273.15
      mass kilogram/liter kg/L
      substance mole/liter mol/L
molality mole/kilogram mol/kg
density kilogram/liter kg/L

Prefixes to the base unit are used in this system to form decimal multiples and submultiples. The preferred multiples and submultiples listed below change the quantity by increments of 103 or 10–3. The exceptions to these recommended factors are within the middle rectangle.

Prefixes and Symbols for Decimal Multiples and Submultiples
Factor Prefix Symbol
1018 exa E
1015 peta P
1012 tera T
109 giga G
106 mega M
103 kilo k
102 hecto h
101 deka da
10-1 deci d
10-2 centi c
10-3 milli m
10-6 micro µ
10-9 nano n
10-12 pico p
10-15 femto f
10-18 atto a

To convert drug concentrations to or from SI units:

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts