CPK Process Capability Calculator
Enter measurement data to automatically calculate CPK, Cp, Cpu, Cpl, PPM and other process capability indices
Enter data and click Calculate
Results and chart will appear here
After installing new tooling, a machining factory needs to verify whether the drilling process capability meets customer requirements (CPK ≥ 1.33). The engineer collects 125 bore diameter measurements, enters USL/LSL, and instantly obtains CPK and PPM estimates to determine production readiness. This tool is also commonly used for initial process studies before Supplier PPAP — AIAG requires an initial CPK ≥ 1.67 for mass production approval.
Measurements: 125 bore diameter readings Mean X̄ = 10.005 mm, Std Dev σ = 0.032 mm USL = 10.10 mm, LSL = 9.90 mm Cpu = (USL - X̄) / (3σ) = (10.10 - 10.005) / (3 × 0.032) = 0.990 Cpl = (X̄ - LSL) / (3σ) = (10.005 - 9.90) / (3 × 0.032) = 1.094 CPK = min(0.990, 1.094) = 0.99 → CPK < 1.33, process not capable → Estimated PPM ≈ 1,350 (1,350 defects per million)
FAQ
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Histogram & Normality Test
CPK assumes normally distributed data. Verify with an Anderson-Darling test first, then return to compute CPK.
Open toolProcess Performance Index
CPK measures short-term capability; PPK reflects long-term actual performance. Comparing both reveals whether special causes affect the process.
Open toolControl Chart (X̄-R)
After confirming capability, use X̄-R control charts to continuously monitor process stability and detect out-of-control signals early.
Open tool