in 1960 the Conference Generale des Poids et Mesures ( CGPM ), which is the international
authority on the metric system, accepted a universal, practical system of units and gave it
the name Le Systeme International d'Unites with the abbreviation SI.
Since then, this most modern and simplest form of the metric system was introduced throughout the world and by 1970's more than 20 countries, including established metric countries, passed legislation adopting the SI system as their only legal system with numerous countries following their example.
Quantity Name Symbol Definition (CGPM)
ength  metre  m  The metre is the length equal to 1 650763,73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2 p10 and 5 d5, of the krypton86 atom.[ 11th CGPM (1960), Resolution 6.] 
mass  kilogram  kg 
The kilogram is the mass of the international prototype of the kilogram recognised by the CGPM and in the
custody of the Bureau International des Poids et Mesures, Sevres, France. [ 1 st CGPM (1889).] 
time  second  s  The second is the duration of 9 192631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium133 atom. [13th CGPM (1967), Resolution 1] 
electric current  ampere  A  The ampere is that constant current which, if maintained in two straight parallel conductors of cu rrent infinite length, of negligible circular crosssection, and placed one metre apart in vacuum would produce . between these conductors a force equal to 2 x 107 newton per metre of length. [CIPM (1946), Resolution 2, approved by the 9th CGPM (1948).] 
thermo dynamic temperature  kelvin  K  The kelvin, unit of thermodynamic temperature, is the fraction 1/273,16 of the thermodynamic temperature of the triple point of water. [13th CGPM (1967), Resolution 4 ] 
amount of substance  mole  mol  The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0,012 kg of carbon 12. [14th CGPM (1971), Resolution 3.] 
luminous intensity  candela  cd  The candela is the luminous intensity, in the perpendicular direction of a surface of 1/600000 square metre of a blackbody at the temperature of freezing platinum under a pressure of 101 325 newtons per square metre. [13th CGPM (1967), Reso'n 5.] 
NOTES:
(i) The unit kelvin and its symbol K are also used to indicate temperature intervals or temperature differences. Besides thermodynamic temperature (symbol T),
expressed in kelvins, Celsius temperature (symbol t) is also used. Celsius temperature is defined by the equation: t = T  T0 where T0 = 273,15 K by definition. Celsius temperature is in general
expressed in degrees Celsius (symbol ^{o}C). The unit "degree Celsius" is therefore equal to the unit "kelvin" and an interval or difference in Celsius temperature is
also expressed in degrees Celsius (^{o}C). Note that the Celsius temperature of the triple point of water is 0,01 ^{o}C, which accounts for the
factor 273,16 in the definition of the kelvin.
(ii) Whenever the mole is used, the elementary entities must be specified, and may be atoms, molecules, ions, electrons, other particles or specified groups of such particles.
(iii) With the object of removing the ambiguity which still occurred in the common use of the word "weight", the 3rd CGPM (1901) declared: "The kilogram is the unit of mass [and not of weight or
of force]; it is equal to the mass of the international prototype of the kilogram."
FACTOR 
...or in full ...

or in
words 
SI
PREFIX 
SI
SYMBOL 
1,0E+24 1,0E+21 1,0E+18 1,0E+15 1,0E+12 1,0E+9 1,0E+6 1,0E+3 1,0E+2 1,0E+1 1,0E1 1,0E2 1,0E3 1,0E6 1,0E9 1,0E12 1,0E15 1,0E18 1,0E21 1,0E24 
1 000 000 000 000 000 000 000 000 1 000 000 000 000 000 000 000 1 000 000 000 000 000 000 1 000 000 000 000 000 1 000 000 000 000 1 000 000 000 1 000 000 1 000 100 10 0,1 0,01 0,001 0,000 001 0,000 000 001 0,000 000 000 001 0,000 000 000 000 001 0,000 000 000 000 000 001 0,000 000 000 000 000 000 001 0,000 000 000 000 000 000 000 001 
septillion sextillion quintillion quadrillion trillion billion million thousand hundred ten tenth hundredth thousandth millionth billionth trillionth quadrillionth quintillionth sextillionth septillionth 
yotta
zetta exa peta tera giga mega kilo hecto deca deci centi milli micro nano pico femto atto zepto yocto 
Y
Z E P T G M k h da d c m µ n p f a z y 
Note: A very common mistake is that the prefix milli stands for a millionth.
WRONG!!
As can be seen from the table above, milli stands for a thousandth. It comes from the French, mille for 1000  they could not use it for the 1000 prefix as that was bagged by
the Greek word, kilo
Note: The prefix hecto to centi are not 'preferred prefix' but referred to as 'other prefix' by SI, though centi
is in common use as in cubic centimetre or cc.

The scientific notation used in the factors column helps to reduce
long numbers to a manageable width. By convention, the number is always shown as a unit [ 1 to 9 ], with decimal places chosen to suit accuracy, and the size of the number is adjusted
by changing the magnitude [E+?]. E+01 means moving the decimal point one space to the right so 1.00E+01 is shorthand for 10, then 1.33E+00 stays at 1.33 and 1.33E01 becomes 0.133.
This format tends to be used when the figure gets longer so E+09 or E09 cuts out a lot of noughts. Don't confuse scientific notation with powers. You can say, quite rightly, that a million is 10 to the power of 6 [ 10^6 or ] but if you confused it with the scientific notation and had 1^7 the answer would be 1 and not a million ! [ you say one times one is one, seven times, and the answer is still one ] So it's all a matter of conventions  if we all follow the same rules then the information is passed correctly from one brain to another which is, after all, the object of writing something down. 
SI DERIVED UNITS EXPRESSED IN TERMS OF SI BASE UNITS AND
SI SUPPLEMENTARY UNITS
Quantity
Name
Symbol
acceleration  metre per second squared  m/s² 
angular acceleration  radian per second squared  rad/s² 
angular momentum  kilogram metre squared per second  kg•m²/s 
angular velocity  radian per second  rad/s 
area  square metre  m² 
cœfficient of linear expansion  1 per kelvin  K ¯¹ 
concentration (of amount of substance)  mole per cubic metre  mol/m³ 
density  kilogram per cubic metre  kg/m³ 
diffusion cœfficient  metre squared per second  m²/s 
electric current density  ampere per square metre  A/m² 
exposure rate (ionising radiation)  ampere per kilogram  A/kg 
kinematic viscosity  metre squared per second  m²/s 
luminance  candela per square metre  cd/m² 
magnetic field strength  ampere per metre  A/m 
magnetic moment  ampere metre squared  A•m² 
mass flow rate  kilogram per second  kg/s 
mass per unit area  kilogram per square metre  kg/m² 
mass per unit length  kilogram per metre  kg/m 
molality  mole per kilogram  mol/kg 
molar mass  kilogram per mole  kg/mol 
molar volume  cubic metre per mole  m³/mol 
moment of inertia  kilogram metre squared  kg•m² 
moment of momentum  kilogram metre squared per second  kg•m²/s 
momentum  kilogram metre per second  kg•m/s 
radioactivity (disintergration rate)  1 per second  s¯¹ 
rotational frequency  1 per second  s¯¹ 
specific volume  cubic metre per kilogram  m³/kg 
speed  metre per second  m/s 
velocity  metre per second  m/s 
volume  cubic metre  m³ 
wave number  1 per metre  m¯¹ 
SI SUPPLIMENTARY UNITS
QUANTITY NAME SYMBOL DEFINITION
plane angle  radian  rad  The radian is the plane angle between two radii of a circle which cut off on the circumference an arc equal in length to the radius 
solid angle  steradian  sr  The steradian is the solid angle which, having it's vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere. 
SI DERIVED UNITS WITH SPECIAL NAMES
Quantity Name Symbol SI Unit Expression in SI Base Un
admittance  siemens  S  ¯¹  m¯²•kg¯¹•s³•A² 
capacitance  farad  F  C / V  m¯²•kg¯¹•s^4•A² 
conductance  siemens  S  ¯¹  m¯²•kg¯¹•s³•A² 
electrical resistance  ohm  V / A  m²•kg•s¯³•A¯²  
electric charge  coulomb  C  A•s  s•A 
electric flux  coulomb  C  A•s  s•A 
electric potential  volt  V  W / A  m²•kg•s¯³•A¯¹ 
electromotive force  volt  V  W / A  m²•kg•s¯³•A¯¹ 
energy  joule  J  N•m  m²•kg•s¯² 
energy flux  watt  W  J/s  m²•kg•s¯³ 
flux of displacement  coulomb  C  A•s  s•A 
force  newton  N  kg•m/s²  m•kg•s¯² 
frequency  hertz  Hz  s¯¹  s¯¹ 
illuminance  lux  lx  lm/m²  m¯²•cd•sr 
impedance  ohm  V / A  m²•kg•s¯³•A¯²  
inductance  henry  H  Wb/A (V•s/A)  m²•kg•s¯²•A¯² 
luminous flux  lumen  lm  cd•sr  cd•sr 
magnetic flux  weber  Wb  V•s  m²•kg•s¯²•A¯¹ 
magnetic flux density  tesla  T  Wb/m²  kg•s¯²•A¯¹ 
magnetic induction  tesla  T  Wb/m²  kg•s¯²•A¯¹ 
magnetic polarization  tesla  T  Wb/m²  kg•s¯²•A¯¹ 
permeance  henry  H  Wb/A (V•s/A)  m²•kg•s¯²•A¯² 
potential difference  volt  V  W / A  m²•kg•s¯³•A¯¹ 
power  watt  W  J/s  m²•kg•s¯³ 
pressure  pascal  Pa  N/m²  m¯¹•kg•s¯² 
quantity of electricity  coulomb  C  A•s  s•A 
quantity of heat  joule  J  N•m  m²•kg•s¯² 
reactance  ohm  V / A  m²•kg•s¯³•A¯²  
stress  pascal  Pa  N/m²  m¯¹•kg•s¯² 
susceptance  siemens  S  ¯¹  m¯²•kg¯¹•s³•A² 
weight  newton  N  kg•m/s²  m•kg•s¯² 
work  joule  J  N•m  m²•kg•s¯² 
NOTES to ABOVE TABLE: 
• The expressions in the fourth coulumn represent the definitions of the respective units in
symbolic form. For instance, the quantity force is defined as the product of mass and acceleration (F=m•a) so the definition of the unit of force, the newton (N) is given by 1 N =
1 kg•m/s²

SI DERIVED UNITS EXPRESSED IN TERMS OF SI DERIVED UNITS WITH SPECIAL NAMES AS WELL AS SI BASE UNITS (ie. the lot!)
Quantity Name Symbol Exp in terms of SI

The mass of over 30 different metals and alloys are listed below. While the data is useful for design, individual samples
will differ. Impurities will often have an influence.
A 1000kg of pure water = 1 cubic metre. Pure water was chosen as the 'base line' for specific gravity and given the value of 1. The specific gravity of all other materials are
compared to water as a fraction heavier or lighter density. For example, beryllium has a specific gravity (sg) of 1.84 (1840 kg/cu.m)
As specific gravity is just a comparison, it can be applied across any units. The density of pure water is also 62.4 lbs/cu.ft (pounds per cubic foot) and if we know that a sample of alumimium
has a sg of 2.5 then we can calculate that its density is 2.5 x 62.4 = 156 lbs/cu.ft.
Note, kg/cu.m divided by 16.02 = lbs/cu.ft
Metal or alloy  kg/cu.m 
aluminium  melted  2560  2640 
aluminium bronze (310% Al)  7700  8700 
aluminium foil  2700 2750 
antifriction metal  9130 10600 
beryllium  1840 
beryllium copper  8100  8250 
brass  casting  8400  8700 
brass  rolled and drawn  8430  8730 
bronze  lead  7700  8700 
bronze  phosphorous  8780  8920 
bronze (814% Sn)  7400  8900 
cast iron  6800  7800 
cobolt  8746 
copper  8930 
delta metal  8600 
electrum  8400  8900 
gold  19320 
iron  7850 
lead  11340 
light alloy based on Al  2560  2800 
light alloy based on Mg  1760  1870 
magnesium  1738 
mercury  13593 
molybdenum  10188 
monel  8360  8840 
nickel  8800 
nickel silver  8400  8900 
platinum  21400 
plutonium  19800 
silver  10490 
steel  rolled  7850 
steel  stainless  7480  8000 
tin  7280 
titanium  4500 
tungsten  19600 
uranium  18900 
vanadium  5494 
white metal  7100 
zinc  7135 