The idea behind the metric system - a system of units based on the metre and the kilogram – arose during the French Revolution when two platinum artefact reference standards for the metre and the kilogram were constructed and deposited in the French National Archives in Paris in 1799 – later to be known as the Metre of the Archives and the Kilogram of the Archives. The French Academy of Science was commissioned by the National Assembly to design a new system of units for use throughout the world, and in 1946 the MKSA system (metre, kilogram, second, ampere) was accepted by the Metre Convention countries. In 1954, the MKSA was extended to include the kelvin and candela. The system then assumed the name the International Systems of Units, SI, (Le Système International d’Unités). The SI system was established in 1960 by the 11th General Conference on Weights and Measures CGPM:

“The International System of Units, SI, is the coherent system of units adopted and recommended by the CGPM”.

At the 14th CGPM in 1971 the SI was again extended by the addition of the mole as base unit for amount of substance. The SI system is now comprised of seven base units, which together with derived units make up a coherent system of units. In addition, certain other units outside the SI system are accepted for use with SI units.

SI BASE UNITS:

Quantity	Base unit	Symbol	Definition
length	metre	m
mass	kilogram	kg
time	second	s
electric current	ampere	A
thermodynamic temperature	kelvin	K
amount of substance	mole	mol
luminous intensity	candela	cd

 

 

 

 

 

 

 

 

The CGPM has adopted and recommended series of prefixes and prefix symbols.

Factor	Prefix name	Symbol	Factor	Prefix name	Symbol
101	deca	da	10-1	deci	d
102	hecto	h	10-2	centi	c
103	kilo	k	10-3	milli	m
106	mega	M	10-6	micro	µ
109	giga	G	10-9	nano	n
1012	tera	T	10-12	pico	p
1015	peta	P	10-15	femto	f
1018	exa	E	10-18	atto	a
1021	zetta	Z	10-21	zepto	z
1024	yotta	Y	10-24	yocto	y