Calculate Cp and Cpk from fill limits, sample mean and standard deviation to assess process centring and spread.
Enter measured lower and upper specification limits, the sample mean and a representative process standard deviation. Capability indices do not prove legal compliance or process stability; review the underlying data and control chart first.
Cp compares specification width with six standard deviations and assumes the process is centred.
Cpk also considers how close the process mean is to the nearest specification limit.
No. The data should come from a stable process and the sampling method, distribution and measurement system must be suitable.
No. Average-quantity rules use their own requirements; capability can support process improvement but is not a legal determination.