Process Capability Index Calculator (Cp, Cpk, Cpm, Pp, Ppk)

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The highest value the output may take and still be considered acceptable.
The lowest value the output may take and still be considered acceptable.
The average (arithmetic mean) of your process measurements.
Within-subgroup standard deviation (s or sigma-hat). Used for Cp and Cpk. If you only have one dataset, use the sample standard deviation.
The ideal process output, used for Cpm. If left equal to the mean, Cpm equals Cpk.
Enable to enter a separate long-term standard deviation for Pp and Ppk calculations.
CpkCapable
1.333

Process capability index - accounts for spread and off-centering

Cp1.333
Cpm1.333
Sigma Level4
Expected Defects63.4PPM
CPU1.333
CPL1.333
Spec Width20
1.333
Not capable<1Marginal1-1.33Capable1.33-1.67Excellent1.67+

Cpk = 1.333: capable process. Meets typical industry minimums.

  • Expected defect rate: approximately 63.4 parts per million (0.0063%).
  • Equivalent sigma level: 4.00.
  • Cp and Cpk are close (1.333 vs 1.333): the process is well-centered within the specification limits.
  • Cpm = 1.333 (Taguchi index, penalising deviation from target T = 100.000).

Next stepConsider monitoring with control charts to detect any drift from this capable state.

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