The following formula is used to calculate COD:
where b is the volume of FAS used in the blank sample, s is the volume of FAS in the original sample, and n is the normality of FAS. If milliliters are used consistently for volume measurements, the result of the COD calculation is given in mg/L.
The COD can also be estimated from the concentration of oxidizable compound in the sample, based on its stoichiometric reaction with oxygen to yield CO (assume all C goes to CO), HO (assume all H goes to HO), and NH (assume all N goes to NH), using the following formula:
:COD = (C/FW)·(RMO)·32
Where 
:C = Concentration of oxidizable compound in the sample,
:FW = Formula weight of the oxidizable compound in the sample,
:RMO = Ratio of the # of moles of oxygen to # of moles of oxidizable compound in their reaction to CO, water, and ammonia
For example, if a sample has 500 Wppm (Weight Parts per Million) of phenol:
:CHOH + 7O → 6CO + 3HO
:COD = (500/94)·7·32 = 1191 Wppm