Enter your process data and get instant Cpk, Ppk and Cp values. Used by quality engineers to check process capability against ISO 9001 and IATF 16949 requirements.
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Cpk 1.37 — process meets ISO 9001 requirements. For IATF 16949 new products, target Cpk ≥ 1.67.
Cpk (Process Capability Index) measures how well a manufacturing process fits within its specification limits, taking into account both the spread and the centering of the process. A higher Cpk means fewer defects and a more capable process.
While Cp only measures the spread of the process relative to the specification width, Cpk also accounts for how centered the process mean is within the tolerance band. A process can have a good Cp but a poor Cpk if it is shifted toward one of the specification limits.
Where x̄ is the process mean, σ is the process standard deviation, USL is the upper specification limit, and LSL is the lower specification limit.
Cpk vs Ppk: Cpk uses within-subgroup standard deviation (short-term variation). Ppk uses overall standard deviation (long-term). Cpk is typically higher. A large gap between them suggests the process mean shifts over time.
| Cpk value | Interpretation | Typical standard | Status |
|---|---|---|---|
| ≥ 1.67 | Excellent — highly capable process | IATF 16949 new products | ✓ Excellent |
| ≥ 1.33 | Good — process is capable | ISO 9001, ongoing production | ✓ Capable |
| 1.00 – 1.33 | Marginal — monitor closely | May require corrective action | ⚠ Marginal |
| < 1.00 | Not capable — producing defects | Immediate action required | ✗ Not capable |
The Cpk calculator is just the beginning. We're building a complete Statistical Process Control platform designed for manufacturing teams who are tired of Excel.
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