Système International d'unites (SI units)

This is the standard set of scientific units used to express quantities. Older texts or articles may use Imperial or c.g.s. (centimetre, gram, second) systems.

Table of SI units

Quantity Dimension SI unit
Length l metre (m)
Mass m kilogram (kg)
Time t second (s) (or h, day, yr, Ma)
Temperature T Kelvin (K)
Area l2 m2
Volume l3 m3
Acceleration l/t m/s
Force m l t-2 kg m/s2 or Newtons (N)
Pressure m l-1 t-2 kg m-1 s-2 or Pascals (Pa)
Work, energy m l2 t-2 kg m2 s-2 or Joules (J)
Power m l-1 t-2 kg m2 s-3 or Watts (W)






Metric Prefixes

Abbreviation Prefix Factor Factor in Scientific Notation
T tera- one trillion 1012
G giga- one billion 109
M mega- one million 106
k kilo- one thousand 103
h * hecto- one hundred 102
da * deka- ten 101
d * deci- one tenth 10-1
c * centi- one hundredth 10-2
m milli- one thousandth 10-3
µ micro- one millionth 10-6
n nano- one billionth 10-9
p pico- one trillionth 10-12

* Note: These elements in the table do not conform to SI standards, which limit units larger or smaller than the basic SI units to multiples of 103 or 10-3.