What this calculator does
Process capability index works out calculates Cp and Cpk from specification limits, the process mean and standard deviation. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
The inputs explained
| Field | What to enter |
|---|---|
| Upper spec limit (USL) | A number. Starts at 10.5. |
| Lower spec limit (LSL) | A number. Starts at 9.5. |
| Process mean (μ) | A number. Starts at 10. |
| Process std deviation (σ) | A number. Starts at 0.15. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with upper spec limit (usl)
Every other input is held at the calculator’s starting values while upper spec limit (usl) varies. Select any row to load that scenario into the calculator.