Cpk Calculator
Enter your tolerance limits and a set of measurements. The calculator returns Cp, Cpk, Pp and Ppk with 95% confidence intervals, checks the data for normality, and says whether the process is capable of holding the tolerance — or why the data cannot say.
Tolerance & measurements
LSL
USL
Subgroup size
| Measurement (mm) | |
|---|---|
Enter at least two measurements and one specification limit.
- Enter the drawing’s lower and upper limits — one is enough for a one-sided feature.
- Enter measurements in production order, one part per row.
- Thirty consecutive parts from an untouched process is the usual study.
How to run this study
Quantify whether a running process can hold a dimension inside its tolerance, and by how much margin. Cpk answers “can this process make good parts consistently?” — Cp shows the potential, Cpk shows what you actually get once centering is accounted for.
Procedure
- 01Let the process reach steady state — mold and discard the first several shots.
- 02Sample at least 30 consecutive parts without touching a single parameter.
- 03Measure the same critical dimension on every part with the same calibrated instrument.
- 04Enter the drawing’s LSL and USL, then each measurement.
- 05Read Cpk against the 1.33 production floor, and compare Cpk to Cp — a gap means the process is off-center.