Convert DPMO/Sigma to Cpk Before discussing how you can convert DPMO (defects per million opportunities) to sigma level and then to a value for Cpk, you must understand what each metric means.

How to Calculate Cpk Cpk is expressed in equation form as: Cpk = min (USL-mean/3σ, mean-LSL/3σ) This means that Cpk is equal to the minimum value of these two calculations.