How to use the Gage R&R calculator
A gage R&R study asks how much of the observed spread belongs to the measurement system rather than the parts. This calculator uses the average and range method from AIAG MSA 4th edition: EV = R̄ × K1 for repeatability, AV = √((X̄diff × K2)² − EV²/(parts × trials)) for reproducibility, GRR = √(EV² + AV²), part variation PV = Rp × K3, and total variation TV = √(GRR² + PV²).
Worked check: with 10 parts, 3 appraisers and 3 trials, entering R̄ 0.0342, X̄diff 0.0445 and Rp 0.8254 returns EV 0.0202, AV 0.0230, GRR 0.0306, PV 0.2597, TV 0.2615, %GRR 11.7% and ndc 11 — the same results published for the worked example in the MSA manual.
Read the verdict as acceptable below 10% GRR, conditionally acceptable from 10% to 30%, and unacceptable above 30%, with ndc of 5 or more needed to tell parts apart. The K1, K2 and K3 constants are fixed by the number of trials, appraisers and parts and cannot be adjusted, and when the term under the square root turns negative the reproducibility is reported as zero. Studies with more than 10 parts, or any study where appraiser-by-part interaction matters, should be run with the ANOVA method instead.
Frequently asked questions
AIAG MSA treats %GRR below 10 percent as acceptable, 10 to 30 percent as conditionally acceptable depending on the application and the cost of improvement, and above 30 percent as unacceptable. The number of distinct categories should also be 5 or more before the system can resolve part-to-part variation.
Repeatability, reported as EV, is the spread when one appraiser measures the same part several times, so it reflects the gage itself. Reproducibility, reported as AV, is the extra variation introduced when the appraiser changes. High EV points to the gage or fixture, while high AV points to method training and work instructions.