SI coherent derived units
Derived units are defined as products of powers of the base units. When the product of powers includes no numerical factor other than one, the derived units are called coherent derived units. The base and coherent derived units of the SI form a coherent set, designated the set of coherent SI units.
When coherent units are used, equations between the numerical values of quantities take exactly the same form as the equations between the quantities themselves. i.e. If only units from a coherent set are used, conversion factors between units are never required.
The expression for the coherent unit of a derived quantity may be obtained from the dimensional product of that quantity by replacing the symbol for each dimension by the symbol of the corresponding base unit.
Each physical quantity has only one coherent SI unit, even if this unit can be expressed in different forms by using some of the special names and symbols. The inverse, however, is not true: in some cases the same SI unit can be used to express the values of several different quantities.
Examples of SI coherent derived units expressed in terms of SI base units
Name  Symbol  Quantity  
square metre  m^{2}  area  
cubic metre  m^{3}  volume  
metre per second  m s^{‑1}  speed, velocity 

metre per second squared  m s^{−2}  acceleration  
cubic metre per second  m^{3} s^{−1}  volumetric flow rate  
reciprocal metre  m^{−1}  wavenumber  
kilogram per cubic metre  kg m^{−3}  density, mass concentration 

kilogram per square metre 
kg m^{−2}  surface density  
cubic metre per kilogram  kg^{−1} m^{3}  specific volume  
kilogram metre per second  kg m s^{−1}  momentum  
kilogram metre squared per second  kg m^{2} s^{−1}  angular momentum  
ampere per square metre 
m^{−2} A  current density  
ampere per metre  m^{−1} A  magnetic field strength  
coulomb per kilogram  kg^{−1} s A  exposure (x and γrays)  
mole per cubic metre  m^{−3} mol  amount concentration, concentration 

candela per square metre 
m^{−2} cd  luminance 