Compute Cp and Cpk indices from your process measurements and specification limits to determine whether your process is capable of consistently meeting requirements. The tool includes a plain-language interpretation guide aligned with Six Sigma decision thresholds.
Process capability analysis answers a deceptively simple question: can this process reliably produce output within the specification limits? Cp tells you whether the process spread is narrow enough relative to the tolerance band. Cpk tells you whether the process is also centred within that band. Together, they separate processes that are merely lucky from processes that are genuinely capable — and they do so with a single pair of numbers that any quality review board can act on.
Enter your upper specification limit, lower specification limit, process mean, and process standard deviation — or paste a sample of raw measurements and let the tool calculate the statistics. The output panel returns Cp, Cpk, the sigma level, the estimated defect rate in parts per million, and a histogram overlaid with the specification limits so you can see the distribution shape. Each result is accompanied by an interpretation note: a Cpk below 1.0 flags an incapable process; between 1.0 and 1.33 indicates marginal capability; above 1.33 is generally acceptable; above 2.0 is Six Sigma territory.
The downloadable Excel template extends the calculator with a control chart tab, a normality check, and a before-and-after comparison layout for documenting improvement projects. It is used widely by quality engineers, Lean Six Sigma practitioners, and operations managers running DMAIC improvement cycles.
For processes with non-normal distributions, multiple characteristics, or automated SPC requirements, contact us to discuss a customised capability study tailored to your production or service environment.
