Quality & Statistics
Gage R&R Calculator
Evaluate your measurement system — repeatability, reproducibility, %GRR, and the number of distinct categories from a crossed study.
What is Gage R&R?
Gage R&R (Repeatability and Reproducibility) is a measurement system analysis that quantifies the amount of variation in your measurement process. It separates measurement variation into:
- Repeatability: same operator, same part, same gage (equipment variation)
- Reproducibility: different operators, same part, same gage (operator variation)
Acceptance criteria
| %GRR | Decision |
|---|---|
| ≤ 10% | Acceptable |
| 10% – 30% | May be acceptable depending on the application, the cost of the gage, and the cost of repair |
| > 30% | Unacceptable — improve the measurement system |
Independently of %GRR, the AIAG MSA manual asks for NDC ≥ 5; below that the gage cannot resolve enough of the process variation for control.
Frequently asked questions
What is NDC (Number of Distinct Categories)?
NDC represents how many distinct groups the measurement system can distinguish within the process variation. NDC ≥ 5 means the gage can resolve enough detail for process control. NDC of 1 means the gage cannot differentiate parts at all.
How should I enter the data?
Enter one row per trial, grouped by operator. For 2 operators × 3 trials on 5 parts, enter 6 rows of 5 values. The order is: Op1-Trial1, Op1-Trial2, Op1-Trial3, Op2-Trial1, Op2-Trial2, Op2-Trial3.
When is Gage R&R required?
IATF 16949 (automotive quality) mandates MSA for all measurement systems referenced in the control plan. The AIAG MSA Reference Manual (4th edition) provides the standard methodology.