What is Rock Mass Rating (RMR)?

Rock Mass Rating (RMR) is a geomechanics classification system developed by Bieniawski (1973, revised 1989). It rates a rock mass on six parameters — UCS, RQD, discontinuity spacing, discontinuity condition, groundwater, and orientation adjustment — producing a score from 0 to 100. It is the most widely used rock classification system in tunneling, mining, and slope engineering worldwide.

What is a good RMR score?

Scores of 81–100 (Class I) indicate very good rock. Scores of 61–80 (Class II) are good rock. Scores of 41–60 (Class III) are fair and require systematic support. Scores below 40 (Classes IV and V) represent poor to very poor rock requiring heavy, immediate support.

What is the difference between RMR76 and RMR89?

RMR89 (Bieniawski 1989) is the current industry standard. It has revised ratings for UCS and RQD, expands discontinuity condition into five sub-parameters, and updates the groundwater rating scale. Always use the 1989 version unless a project specifically requires the earlier edition.

How does RMR relate to the Q-System?

Both are empirical rock classification tools. The common correlation is: RMR ≈ 9 × ln(Q) + 44. On important projects, calculate both independently and compare. Significant divergence signals unusual site conditions worth investigating further.

How do I calculate RQD without core drilling?

Use Palmstrom's formula: RQD = 115 − 3.3 × Jv, where Jv is the number of joints per cubic meter. Alternatively use Priest and Hudson (1976): RQD = 100 × e^(−0.1λ) × (0.1λ + 1), where λ is mean joint frequency per meter.

Is this RMR calculator suitable for professional reports?

This calculator correctly implements Bieniawski 1989 and supports professional work as a computation aid. All input parameters must be assessed by a qualified geotechnical or mining engineer from actual field investigations and lab tests before use in final design.

Disclaimer – RMR Calculator

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Disclaimer

Rock Mass Rating Calculator · Last updated: April 28, 2026

Important — Please Read Before Using

The Rock Mass Rating (RMR) Calculator provided on this website is intended for educational and preliminary engineering purposes only. It must not be used as the sole basis for any final engineering design, construction decision, or safety-critical application.

1. No Professional Engineering Advice

The results produced by this calculator do not constitute professional geotechnical or engineering advice. All site-specific assessments must be reviewed, verified, and approved by a licensed Professional Engineer (PE) or qualified geotechnical specialist with relevant rock mechanics experience.

2. Accuracy of Results

This calculator implements the Bieniawski 1989 Rock Mass Rating methodology. However, the accuracy of any RMR result depends entirely on the quality of the input data provided by the user. We are not responsible for:

Errors resulting from incorrect or estimated input parameters
Results based on inadequate site investigation
Decisions made using calculator output without professional review

3. Field Data Required

Rock Mass Rating must be determined from actual field investigation and laboratory testing — including core drilling, RQD logging, lab UCS testing, and direct observation of groundwater and joint conditions. Do not estimate input parameters without proper site data.

4. No Liability

RMR Calculator, its owners, and contributors accept no liability for any loss, damage, injury, or consequence arising directly or indirectly from the use of this tool or reliance on its results. Use of this website is entirely at your own risk.

5. Third-Party References

This tool is based on the published work of Z.T. Bieniawski (1989). We make no claim of affiliation with the original author or publisher. All engineering standards and classifications referenced belong to their respective authors and organizations.

✅ This tool is correct when used properly with real field data and professional oversight. It is trusted by engineers and students worldwide for preliminary rock classification work.