SI units

The International System of Units (abbreviated SI from French: Le Système international d'unités) is the modern form of the metric system and is the world's most widely used system of measurement, used in both everyday commerce and science.

 It comprises a coherent system of units of measurement built around:

  • seven base units, 
  • 22 named and 
  • an indeterminate number of unnamed coherent derived units, and 
  • a set of prefixes that act as decimal-based multipliers. 

It is part of the International System of Quantities.

Scientific notation is also typically used to describe very large or small values.

The base units are:

  • metre - distance - m
  • kilogram - mass - kg
  • second - time - s
  • ampere - electric current - A
  • kelvin - temperature - K
  • mole - amount of substance - mol
  • candela - luminous intensity - cd


Standard prefixes for the SI units of measure

For units larger than 1 

da - 101  deca

h - 102 hecto

k -  103 kilo

M - 106 mega

G - 109 giga

T - 1012 tera  

P - 1015 peta 

E - 1018 exa

Z - 1021 zetta

Y - 1024 yotta 

For units less than 1

d - 10-1  deci

c - 10-2 centi

m -  10-3 milli

µ - 10-6 micro

n - 10-9 nano

p - 10-12 pico  

f - 10-15 femto 

a - 10-18 atto

z - 10-21 zepto

y - 10-24 yocto 


source:  http://en.wikipedia.org/w/index.php?title=International_System_of_Units&oldid=614223948