DPMO = 
Statistics for DPU and Pareto charts are derived from the basic defect per unit calculation:
DPU = defects / # of samples
The most common derivation is defects per million or DPM.
DPM = defects / # of samples * 1 million
This formula can be extended to include defects per thousand (DPK) and defects per billion (DPB).
Users who want to factor in the complexity of the process can do so by recording the number of opportunities per sample with the part standard. This number is used to calculate the number of defects per million opportunities.
DPMO =
This formula can be extended to include defects per thousand opportunities (DPKO) and defects per billion opportunities (DPBO).
Instead of calculating defects per million, you may also calculate parts (defective units) per million (PPM). This method is only applicable if you can have more than one defect per defective unit. (If each defect causes one defective unit, then DPM will always equal PPM.) For information on choosing whether you can have more than one defect on each defective part, see Set NCU to number of defects.
PPM = defective units / # of samples * 1 million
This formula can be extended to include defective units per thousand (PPK) and defective units per billion (PPB).