Process Capability Index Calculator

The capability index of a process measures the percentage of non-conforming values produced by the process. Denoted as Cpk, it is defined as:
Cpk = min[ (USL – mean) /3σ , (mean – LSL) /3σ ]
  • USL is the upper specification limit
  • LSL is the lower specification limit
  • mean is the process mean
  • σ is the process standard deviation
To find the process capability index, simply fill in the values below and then click the “Calculate” button.

Capability Index (Cpk): 0.4505


Cpk = min[ (USL – mean) /3σ , (mean – LSL) /3σ ]

Cpk = min[ (1712) /3*3.7 , (126) /3*3.7 ]

Cpk = 0.4505

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