Statistics

Process Capability Index Calculator

Find Cp and Cpk for a manufacturing process.

Calculated Output

Cp 1.111

Cpk 0.8889

Formula: Cp = (USL − LSL)/(6σ); Cpk = min(...)/(3σ)

Step-by-Step Breakdown

1. Values used:

2. Upper spec limit = 110

3. Lower spec limit = 90

4. Process mean = 102

5. Process SD = 3

7. Cp = 1.111

8. Cpk = 0.8889

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The math behind it

Cp = (USL − LSL)/(6σ) ignores centering; Cpk also accounts for how off-center the mean is. ≥1.33 is usually 'capable'.

USL 110, LSL 90, mean 102, σ 3 → Cp 1.11, Cpk 0.89.

Cp vs Cpk?

Cp measures potential capability; Cpk reflects actual performance with the current mean.