Gauge Capability Study

Table of Contents

What is a Gauge Capability Study?

A gauge capability study determines whether a measurement gauge has sufficient resolution and precision for the part tolerance it measures. It computes Cp/Cpk capability indices and the gauge discrimination ratio to give you a clear answer: "Is this gauge good enough for this job?"

1Setup

Enter gauge information (ID, type, resolution), the unit of measurement, and the specification limits (USL, LSL). Optionally provide a target value for Cpm calculation.

2Data Entry

Enter repeated measurements of the same reference part. A minimum of 25 readings is recommended for reliable capability analysis. More readings give better statistical confidence.

3Analysis

The tool computes Cp, Cpk, Pp, Ppk indices and the gauge discrimination ratio. A combined verdict tells you whether the gauge is suitable, has insufficient resolution, is too variable, or is unsuitable for the tolerance.

4View & Export

Review the full results, download a PDF report, or start a new study. AI coaching can explain the results and recommend improvements.

Understanding Results

Suitable Cpk >= 1.33 and discrimination ratio >= 10. The gauge is appropriate for this tolerance.

Resolution Insufficient Cpk >= 1.33 but discrimination ratio is below 10. Consider a gauge with finer resolution.

Too Variable Discrimination ratio >= 10 but Cpk is below 1.33. Investigate measurement technique or gauge condition.

Unsuitable Both Cpk and discrimination ratio are insufficient. A different gauge is needed.

Key Terms

Cpk: Process capability index accounting for process centering. Cpk >= 1.33 indicates a capable process.
Cp: Potential process capability index (assumes centered process). Cp = (USL - LSL) / (6 * sigma).
Disc. Ratio: Gauge discrimination ratio = Tolerance / Resolution. Measures how many distinct levels the gauge can detect within the tolerance.
Rule of Ten: The gauge resolution should be at most 1/10th of the tolerance (discrimination ratio >= 10).

Tip:

For best results, take all measurements under the same conditions (same operator, same environment) to isolate gauge variation from other sources.

Start Capability Study