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RMR Worksheet Calculator

Add up the five Bieniawski RMR89 parameter ratings and apply the discontinuity-orientation adjustment to get the Rock Mass Rating and its class. Used by geotechnical engineers and engineering geologists to classify rock masses for tunnels, slopes and foundations.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Read each parameter rating (R1 strength, R2 RQD, R3 spacing, R4 discontinuity condition, R5 groundwater) off the standard Bieniawski tables and enter the points.
  2. Enter the orientation adjustment R6 (0 for very favourable, down to −60 for very unfavourable) — leave blank for 0.
  3. Read the basic RMR, final RMR89, rock-mass class and the indicative cohesion/friction ranges.

How it works

The RMR89 system rates a rock mass on five parameters: uniaxial compressive strength (0–15), RQD (3–20), discontinuity spacing (5–20), condition of discontinuities (0–30) and groundwater (0–15). Summing them gives the basic RMR out of 100.

A sixth term, R6, adjusts for how favourably the discontinuities are oriented relative to the excavation — it ranges from 0 down to −60 and is subtracted from the basic value. The final RMR maps to five classes: I very good (81–100), II good (61–80), III fair (41–60), IV poor (21–40) and V very poor (<21), each with indicative cohesion and friction-angle ranges.

Worked example

Fair-to-good jointed rock. R1 12, R2 17, R3 15, R4 25, R5 10 sum to a basic RMR of 79. With an orientation adjustment R6 of −5 the final RMR89 is 74, placing the rock mass in Class II (good rock), with typical cohesion 300–400 kPa and friction 35–45°.

Common mistakes

  • Entering raw measured values (e.g. UCS in MPa or RQD %) instead of the assigned rating points from the tables.
  • Making R6 positive — the orientation adjustment is zero or negative in RMR89.
  • Confusing RMR76 and RMR89 rating bands; this worksheet uses the 1989 groundwater and condition ratings.

Frequently asked questions

What is a good RMR value?

RMR 61–80 is Class II (good rock) and 81–100 is Class I (very good). Class III (41–60) is fair, and anything below 41 is poor or very poor and usually needs more support.

Is this RMR76 or RMR89?

It uses the RMR89 (Bieniawski 1989) ratings, which have a maximum basic RMR of 100 and the updated groundwater and discontinuity-condition tables.

Why is the orientation adjustment negative?

R6 penalises unfavourable discontinuity orientation. It is 0 for very favourable conditions and becomes more negative (to about −12 for tunnels, or −60 for very unfavourable slopes) as orientation worsens.

Can I get cohesion and friction from RMR?

Bieniawski's table gives indicative ranges per class (e.g. Class II ≈ c 300–400 kPa, φ 35–45°). Treat these as first-pass guidance, not design values.

How does RMR relate to GSI and Q?

GSI ≈ 1.5·RMR89 − 10 (or RMR89 − 5) for RMR > 18, and there are approximate correlations to Barton's Q. Use the GSI Helper and Q System Worksheet for those.

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