The simplest case refers to the formation of a strictly linear polymer by the reaction (usually by condensation) of two monomers in equimolar quantities. An example is the synthesis of nylon-6,6 whose formula is 
from one mole of hexamethylenediamine, , and one mole of adipic acid, . For this case
In this equation
* is the number-average value of the degree of polymerization, equal to the average number of monomer units in a polymer molecule. For the example of nylon-6,6   ( diamine units and  diacid units).
* is the extent of reaction (or conversion to polymer), defined by
** is the number of molecules present initially as monomer
** is the number of molecules present after time . The total includes all degrees of polymerization: monomers, oligomers and polymers.
This equation shows that a high monomer conversion is required to achieve a high degree of polymerization.  For example, a monomer conversion, , of 98% is required for  = 50, and  = 99% is required for  = 100.