The metric system is based on the number ten. Prefixes determine the power of ten. Some prefixes are for numbers greater than one and others are used for numbers less than 1.
Prefix 
Abbreviation symbol 
Power of ten (Scientific notation) 
Power of ten (real number) 
Yotta 
Y 
10^{24} 
1,000,000,000,000,000,000,000,000 
Zetta 
Z 
10^{21} 
1,000,000,000,000,000,000,000 
Exa 
E 
10^{18} 
1,000,000,000,000,000,000 
Peta 
P 
10^{15} 
1,000,000,000,000,000 
Tera 
T 
10^{12} 
1,000,000,000,000 
Giga 
G 
10^{9} 
10,000,000,000 
Mega 
M 
10^{6} 
1,000,000 
myria 
my 
10^{4} 
10,000 
kilo 
k 
10^{3} 
1000 
hecto 
h 
10^{2} 
100 
daka 
da 
10^{1} 
10 
 
Base unit 1 
10^{0} = 1 
1 
deci 
d 
10^{1} 
0.1 
centi 
c 
10^{2} 
0.01 
milli 
m 
10^{3} 
0.001 
micro 
u 
10^{6} 
0.000001 
nano 
n 
10^{9} 
0.000000001 
pico 
p 
10^{12} 
0.0000000000001 
femto 
f 
10^{15} 
0.0000000000000001 
atto 
a 
10^{18} 
0.0000000000000000001 
zepto 
z 
10^{21} 
0.0000000000000000000001 
yocto 
y 
10^{24} 
0.0000000000000000000000001 
The seven basic units and their symbols and definitions are listed in the table below.
Variable 
Metric / SI symbol (name) 
definition 
length 
m (meter) 
The metre is the basic unit of length. It is the distance light travels, in a vacuum, in 1/299792458th of a second.

time 
s(second) 
The second is the basic unit of time. It is the length of time taken for 9192631770 periods of vibration of the caesium133 atom to occur.

temperature 
K (Kelvin) 
The kelvin is the basic unit of temperature. It is 1/273.16th of the thermodynamic temperature of the triple point of water. It is named after the Scottish mathematician and physicist William Thomson 1st Lord Kelvin (18241907).

mass 
kg (kilogram) 
The kilogram is the basic unit of mass. It is the mass of an international prototype in the form of a platinumiridium cylinder kept at Sevres in France. It is now the only basic unit still defined in terms of a material object, and also the only one with a prefix[kilo] already in place.

Electric current 
A (ampere) 
The ampere is the basic unit of electric current. It is that current which produces a specified force between two parallel wires which are 1 metre apart in a vacuum.It is named after the French physicist Andre Ampere (17751836).

Light intensity 
Cd (Candela) 
The candela is the basic unit of luminous intensity. It is the intensity of a source of light of a specified frequency, which gives a specified amount of power in a given direction. 
Amount of substance 
mol (mole) 
The mole is the basic unit of substance. It is the amount of substance that contains as many elementary units as there are atoms in 0.012 kg of carbon12.

There are many derived variables. These variables come from combinations of the seven basic units. The table below shows some of them.
variable 
Unit (name/abbreviation) 
area 
Square meters (m^{2}) 
volume 
Cubic meters (m^{3}) 
density 
Kg / m^{3} 
speed 
m /s 
acceleration 
m /s^{2} 
Specific volume 
m^{3} / kg 
concentration 
Mol / m^{3} 
frequency 
Hertz (Hz) = s^{1} 
force 
Newton (N) = kg m/s^{2} 
pressure 
Pascal (Pa) = 1N /m^{2} 
power 
Watt (W) = J/s = kg m^{2} / s^{3} 
Energy (heat) 
Joule (J) = kg m^{2} / s^{2} 
Electric charge 
Coulomb (c) = s A 
Electric potential 
Volt (V) = W / A 
Electric resistance 
Ohm ( ) = V / A 