Gage R&R (Repeatability and Reproducibility) evaluates a measurement system's variation. Repeatability is variation when the same operator measures the same part repeatedly. Reproducibility is variation between different operators measuring the same part.

What is an acceptable %GRR?

Less than 10% GRR is considered excellent. 10-30% is conditionally acceptable depending on application. Greater than 30% is unacceptable — the measurement system needs improvement.

ndc (number of distinct categories) indicates how many groups of parts the measurement system can reliably distinguish. ndc ≥ 5 is acceptable. ndc = 1.41 × (Part variation / GRR).

How many parts and operators are needed?

A typical Gage R&R study uses 10 parts, 3 operators, and 2-3 trials per combination. Minimum is 5 parts and 2 operators with 2 trials. More parts and trials improve the study's statistical power.

What is the difference between R&R and ANOVA methods?

The Range (R&R) method uses average ranges to estimate variation — simpler but less precise. ANOVA decomposes total variation statistically and can also estimate operator-by-part interaction. ANOVA is preferred for more accurate results.

Free Engineering Tool

Gage R&R Calculator

Evaluate measurement system variation per ISO 5725. Enter measurements for multiple parts, operators, and trials. Calculate repeatability, reproducibility, %GRR, and ndc.

ISO 5725MSA%GRR & ndc

Results

%GRR (of Total Variation)

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Repeatability (EV)

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Reproducibility (AV)

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Part Variation (PV)

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ndc (Distinct Categories)

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%GRR Criteria

< 10% — Excellent. Measurement system acceptable.
10–30% — Conditionally acceptable. May be acceptable depending on application and cost.
> 30% — Unacceptable. Measurement system needs improvement.

Number of Distinct Categories (ndc)

ndc ≥ 5 indicates the measurement system can adequately distinguish between parts.

Gage R&R Calculator | ISO 5725 | Measurement System Analysis

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Results

%GRR Criteria

Number of Distinct Categories (ndc)