Question 1

What Cpk value is acceptable?

Accepted Answer

Cpk >= 1.33 is the industry standard for existing processes. For new or safety-critical processes, Cpk >= 1.67 is often required. Cpk = 1.0 means the process barely fits within spec limits, with about 0.27% defects (2700 PPM).

Question 2

What is the difference between Cp and Cpk?

Accepted Answer

Cp measures potential capability assuming the process is perfectly centered. Cpk measures actual capability by accounting for how far the mean has shifted from center. Cpk is always <= Cp. When Cpk = Cp, the process is perfectly centered.