For a continuous stirred-tank reactor (CSTR), the following relationship applies:
where:
* is the reactor volume
* is the molar flow rate per unit time of the entering reactant A
* is the conversion of reactant A
* is the rate of disappearance of reactant A per unit volume per unit time
For a plug flow reactor (PFR), the following relationship applies:
If  is plotted as a function of , the required volume to achieve a specific conversion can be determined given an entering molar flow rate.
The volume of a CSTR necessary to achieve a certain conversion at a given flow rate is equal to the area of the rectangle with height equal to  and width equal to .
The volume of a PFR necessary to achieve a certain conversion at a given flow rate is equal to the area under the curve of  plotted against .