| Measure | Value |
|---|---|
| PPM, two-sided, centred | 26.7 |
| PPM, one side only | 13.3 |
| Yield (two-sided) | 99.99733 % |
| Sigma level Z = 3 · Cpk | 4.20 |
| Long-term PPM with 1.5 σ shift | 3,467 |
| Distance mean to nearest limit | 4.20 σ |
What Cpk 1.40 means
Cpk compares the distance between the process mean and the nearest specification limit with three standard deviations. At Cpk 1.40 the nearest limit is 4.20 standard deviations away from the mean. The PPM values above assume a normal distribution and a stable process; for skewed data use a fitted distribution in the capability study.
Meets the common requirement for ongoing production (1.33), but not the 1.67 often asked for special characteristics or initial studies. Remember that a Cpk calculated from a small sample is uncertain: with 30 values the 95 % confidence interval is roughly ±0.4. Plan the number of parts with the sample size calculator.
Compare with other values
Cpk 1.33Cpk 1.50Convert any value · What is a good Cpk?
Frequently asked questions
How many PPM is Cpk 1.40?
For a normal, stable process centred between two specification limits, Cpk 1.40 corresponds to 26.7 PPM (defects outside both limits). If only one limit matters or the process sits at one side, it is 13.3 PPM.
What sigma level is Cpk 1.40?
Z = 3 × Cpk = 4.20. With the Six Sigma 1.5 sigma long-term shift, the expected long-term defect rate is about 3,467 PPM.
Is Cpk 1.40 good?
Meets the common requirement for ongoing production (1.33), but not the 1.67 often asked for special characteristics or initial studies.