| Measure | Value |
|---|---|
| DPMO long term (1.5 σ shift) | 6,210 |
| Yield long term | 99.37903 % |
| PPM without shift (one side) | 31.7 |
| Equivalent Cpk (short term) | 1.33 |
| Equivalent Ppk (long term) | 0.83 |
Where the numbers come from
The sigma level is the number of standard deviations between the process mean and the nearest specification limit, measured on short-term data. Six Sigma practice assumes the mean drifts by up to 1.5 σ over time, so the long-term defect rate is calculated at 4 − 1.5 = 2.5 σ. Automotive capability studies usually report Cpk and Ppk without this shift; see Cpk, PPM and sigma level explained.
Other sigma levels
Frequently asked questions
How many defects is 4 sigma?
6,210 DPMO long term, assuming the usual 1.5 sigma shift of the mean. Without that shift the one-sided defect rate is 31.7 PPM.
What Cpk is 4 sigma?
Cpk = sigma level / 3 = 1.33 short term; the long-term Ppk after the 1.5 sigma shift is 0.83.