Rock Mass Rating Calculator
Free online RMR calculator based on the Bieniawski 1989 classification system. Enter your rock mass parameters below and instantly determine rock class, stand-up time, cohesion, and friction angle.
Enter Rock Mass Parameters
All six Bieniawski 1989 parameters. Results update in real time.
1 Uniaxial Compressive Strength (UCS)
Intact rock strength measured via laboratory testing or estimated from point load index.
2 Rock Quality Designation (RQD) ?
Percentage of intact core pieces longer than 100 mm in a core run.
3 Spacing of Discontinuities
Average spacing between adjacent discontinuities measured along the tunnel axis or borehole.
4 Condition of Discontinuities
Assessed through five sub-parameters. Maximum combined rating is 30.
5 Groundwater Conditions
General conditions observed at the tunnel face or in the borehole.
6 Discontinuity Orientation Adjustment
Select the application type, then rate how favorable the joint orientations are relative to the excavation.
RMR Result
| Basic RMR (before adjustment) | 0 |
| Orientation Adjustment | 0 |
| Total Adjusted RMR | 0 |
| Rock Class | Class V |
| Description | Very Poor Rock |
| Stand-up Time | 30 min for 1 m span |
| Cohesion | < 100 kPa |
| Friction Angle | < 15° |
RMR Classification Reference Table
The Bieniawski 1989 classification groups rock masses into five classes based on total RMR score. This table summarizes the engineering properties associated with each class.
| Class | RMR Score | Description | Stand-up Time | Cohesion | Friction Angle |
|---|---|---|---|---|---|
| I | 81–100 | Very Good Rock | 20 yrs / 15 m span | > 400 kPa | > 45° |
| II | 61–80 | Good Rock | 1 yr / 10 m span | 300–400 kPa | 35–45° |
| III | 41–60 | Fair Rock | 1 wk / 5 m span | 200–300 kPa | 25–35° |
| IV | 21–40 | Poor Rock | 10 hrs / 2.5 m span | 100–200 kPa | 15–25° |
| V | ≤ 20 | Very Poor Rock | 30 min / 1 m span | < 100 kPa | < 15° |
How to Use This Rock Mass Rating Calculator
This free online Rock Mass Rating calculator implements the complete Bieniawski 1989 classification system. It is designed for geotechnical engineers, mining engineers, geology students, and tunnelling consultants who need a quick, reliable way to calculate RMR scores from field data or laboratory test results.
To use the calculator, work through each of the six parameters in order. Start with the Uniaxial Compressive Strength of the intact rock, which you can determine from laboratory UCS tests, point load index tests, or Schmidt hammer readings. Select the range that matches your measured or estimated value from the dropdown menu.
Next, enter the Rock Quality Designation (RQD) as a percentage. If you have core logs, calculate RQD as the sum of intact pieces longer than 100 mm divided by the total core run length. If you do not have core, you can estimate RQD from the volumetric joint count using the Palmstrom formula on our RQD Calculator page.
For the spacing of discontinuities, select the range that best matches the average spacing between adjacent joints, bedding planes, or other discontinuities measured in the field. For the condition of discontinuities, assess each of the five sub-parameters independently: persistence, aperture, roughness, infilling material, and degree of weathering. Each sub-parameter has its own rating scale.
Rate the groundwater conditions based on your observations at the tunnel face, in the borehole, or at the slope face. Finally, select your application type (tunnel, slope, or foundation) and rate how favorable the discontinuity orientations are relative to your excavation direction.
The calculator sums all parameter ratings in real time, applies the orientation adjustment, and displays the total RMR score along with the corresponding rock class, stand-up time, cohesion, and friction angle. You can download a PDF report of your results or copy them to your clipboard for use in reports. Your inputs are automatically saved in your browser so you can return to them later.
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RMR Calculator — Complete Guide
5 pagesRMR Complete Guide
Full Bieniawski 1989 guide — all 6 parameters, classification table, applications, and comparisons
RMR Parameters Explained
Deep dive into all 6 rating criteria with full tables and field assessment tips
RMR Classification Table
Rock Classes I to V — score ranges, engineering behaviour, and support implications
How to Calculate RMR
Step-by-step guide with field checklist and printable data recording sheet
RMR Worked Examples
3 fully solved problems — granite tunnel, shale slope, and limestone foundation
All Rock Mass Tools
Overview of all free geotechnical calculators with a decision guide for when to use each
Q-System Calculator
Barton 1974 rock mass quality — calculate Q value, classification, and RMR correlation
RQD Calculator
Rock Quality Designation from core pieces or volumetric joint count — feeds directly into RMR
Geotechnical Guides
4 pagesAll Geotechnical Guides
Educational guides on rock mass assessment, classification, and engineering applications
What is Rock Mass Rating?
RMR definition, history from 1973 to 1989, intact rock vs rock mass, and who uses it
RMR Field Assessment Guide
How to measure each parameter on site — Schmidt hammer, core logs, ISRM guidance
Tunnel Support Design from RMR
Bieniawski 1989 support table — rock bolts, shotcrete, steel sets by RMR class
Frequently Asked Questions
Rock Mass Rating (RMR) is a geomechanical classification system developed by Professor Z.T. Bieniawski in 1973 and updated in 1989. It assigns a numerical rating from 0 to 100 based on six parameters: uniaxial compressive strength, rock quality designation (RQD), discontinuity spacing, condition of discontinuities, groundwater conditions, and joint orientation adjustment. The total score determines the rock class from I (very good) to V (very poor), which guides engineering decisions for tunnels, slopes, and foundations. RMR is one of the most widely used rock mass classification systems in geotechnical and mining engineering worldwide.
This calculator implements the Bieniawski 1989 version of the Rock Mass Rating system, which is the most widely used and internationally accepted revision. The 1989 version refined the rating criteria from the original 1973 system, providing clearer guidelines for assessing discontinuity conditions through five sub-parameters (persistence, aperture, roughness, infilling, and weathering) and updated orientation adjustment values for tunnels, slopes, and foundations. This is the version referenced in most modern geotechnical textbooks and engineering standards.
An RMR value of 81–100 is classified as Class I (Very Good Rock), indicating excellent rock mass conditions with predicted stand-up times of 20 years for a 15-meter span. Values of 61–80 (Class II, Good Rock) are also favorable, with stand-up times of about 1 year for a 10-meter span. Class III (41–60, Fair Rock) represents moderate conditions. Values below 40 indicate poor to very poor conditions that require significant engineering support measures such as steel sets, heavy shotcrete, and closely spaced rock bolts.
While both are rock mass classification systems used in underground excavation design, they differ in approach. RMR uses an additive scoring method, summing six parameters to produce a rating from 0 to 100. The Q-system (Barton, Lien, and Lunde 1974) uses a multiplicative formula Q = (RQD/Jn) × (Jr/Ja) × (Jw/SRF), producing values spanning several orders of magnitude from 0.001 to 1000. RMR is more commonly used in civil engineering applications and slope stability, while the Q-system is prevalent in Scandinavian tunnelling practice. Both systems can be correlated using the empirical relationship RMR ≈ 9 ln(Q) + 44.
Yes, RMR can be applied to slope stability assessment, but you must use the slope-specific orientation adjustment values, which range from 0 to −60 rather than the tunnel values of 0 to −12. This calculator supports slope orientation adjustments by selecting the "Slopes" application type in Parameter 6. For more detailed slope analysis, many engineers extend the basic RMR into the Slope Mass Rating (SMR) system developed by Romana in 1985, which adds specific correction factors for the geometric relationship between joint orientations and the slope face.