Gage R&R Calculator: Is Your Measuring System Good Enough?

By Robert Low, Director, Lead Auditor & BRCGS Approved Trainer

You calibrate your gauges, but that does not tell you whether your measuring system can actually tell good product from bad. That is what a Gage R&R study answers. My free Gage R&R calculator estimates %GRR and the number of distinct categories and gives you a verdict.

What the Gage R&R (Quick) Does

Gage R&R stands for repeatability and reproducibility. Repeatability is whether the same person measuring the same item gets the same answer. Reproducibility is whether different people get the same answer. Together they tell you how much of the variation you see is real product variation and how much is just measurement noise.

The common guide from the automotive quality manual is that under 10 percent GRR is acceptable, between 10 and 30 percent is marginal and over 30 percent is not acceptable. The number of distinct categories, or NDC, should be at least 5. My tool gives you both with those verdicts.

How to Use It

1. Open Gage R&R (Quick) on the free resources page.
2. Enter your study data from several parts, operators and repeat readings.
3. Read %GRR and NDC.
4. Act on the verdict: fix the method, the gauge or the training.

Where It Helps Beyond Certification

This is a calibration and defensibility tool. If a customer rejects your product on a dimension, or you reject theirs, you need to know whether the measurement itself can be trusted. A passing Gage R&R is strong evidence that it can.

It is also a cheap way to find training gaps. When reproducibility is the problem and not the gauge, the cause is usually that operators measure differently, and that is a method and training fix.

Where Sites Get Caught Out

Do not pick your best operator and your easiest parts. Use parts that span the real range, including some near the limits, and use the people who really do the measuring.