The Lab · Quality

Process Capability (Cpk)

Enter your tolerance limits and a set of measurements. The tool returns Cp, Cpk, and whether the process is capable of holding the tolerance.

Tolerance & measurements
LSL
USL
Measurement
Enter LSL, USL, and at least two measurements.

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

  1. 01Let the process reach steady state — mold and discard the first several shots.
  2. 02Sample at least 30 consecutive parts without touching a single parameter.
  3. 03Measure the same critical dimension on every part with the same calibrated instrument.
  4. 04Enter the drawing’s LSL and USL, then each measurement.
  5. 05Read Cpk against the 1.33 production floor, and compare Cpk to Cp — a gap means the process is off-center.