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Rock Mass Rating Calculator

Bieniawski 1989 RMR

6 parameters

Rock class & stand-up time

Rock Mass ParametersFree - Instant

Uniaxial Compressive Strength (UCS)12 pts

> 250 MPa (Very strong)+15100–250 MPa (Strong)+1250–100 MPa (Moderate)+725–50 MPa (Weak)+45–25 MPa (Very weak)+21–5 MPa (Very weak)+1< 1 MPa (Extremely weak)+0

Rock Quality Designation (RQD)17 pts

90–100% (Excellent)+2075–90% (Good)+1750–75% (Fair)+1325–50% (Poor)+8< 25% (Very poor)+3

Spacing of Discontinuities10 pts

> 2 m (Very wide)+200.6–2 m (Wide)+150.2–0.6 m (Moderate)+100.06–0.2 m (Close)+8< 0.06 m (Very close)+5

Condition of Discontinuities20 pts

Very rough, unweathered, tight+30Slightly rough, slightly weathered+25Slightly rough, highly weathered+20Slickensided or gouge < 5 mm+10Soft gouge > 5 mm or open > 5 mm+0

Groundwater Conditions10 pts

Completely dry+15Damp (minor seepage)+10Wet (moderate flow)+7Dripping (high flow)+4Flowing (very high)+0

Joint Orientation Adjustment-5 pts

About the RMR System

The Bieniawski Rock Mass Rating (RMR) system classifies rock by summing ratings for five primary parameters (maximum 100 points), then applying a joint orientation adjustment (0 to -12). The final score determines rock class, stand-up time, and recommended support for tunnels and slopes.

Basic RMR = UCS + RQD + Spacing + Condition + GW
Total RMR = Basic RMR + Joint Orientation Adj.
Range: 0 (worst) to 100 (best)

Who Is This Calculator For?

The Bieniawski RMR system is used wherever engineers need a rapid, standardized assessment of rock mass quality, from tunnel feasibility studies to open-pit slope design. This tool implements the complete 1989 classification, including the joint orientation adjustment.

Geotechnical Engineers

Classify rock mass quality for tunnel support design and underground excavation planning.

Mining Engineers

Assess excavation stability and determine initial support requirements for mining drifts.

Civil Engineers

Evaluate rock cuts along highways and infrastructure corridors for slope stability.

Site Investigation Teams

Process borehole logs and lab results into a standardized RMR classification.

Graduate Students

Learn the six RMR parameters and practice applying Bieniawski 1989 to field data.

Project Owners

Understand what an RMR score means for stand-up time and support requirements.

When Should You Use It?

After borehole logging and laboratory uniaxial compressive strength testing
During feasibility assessment for a tunnel, cavern, or underground opening
When developing initial rock bolt and shotcrete support designs
For preliminary slope stability assessment in open-cut or highway work
Comparing site conditions against published RMR benchmarks and case studies

Example Calculations

Example 1: Hard granite tunnel heading

UCS 100–250 MPa: +12 pts
RQD 75–90% (Good): +17 pts
Spacing 0.2–0.6 m: +10 pts
Condition: slightly rough, slightly weathered: +25 pts
Groundwater: damp: +10 pts
Basic RMR = 74 | Joint orientation: favorable −2
Total RMR = 72, Class II Good Rock (1 year stand-up @ 10 m)

Example 2: Weathered shale road cut

UCS 25–50 MPa: +4 pts
RQD 25–50% (Poor): +8 pts
Spacing < 0.06 m (Very close): +5 pts
Condition: slickensided joints: +10 pts
Groundwater: wet: +7 pts
Basic RMR = 34 | Joint orientation: unfavorable −10
Total RMR = 24, Class IV Poor Rock (10 hrs stand-up @ 2.5 m)

Common Mistakes to Avoid

Assigning a single RMR to a site without zoning by geological domain: different rock units need separate classifications

Confusing RQD with core recovery percentage: RQD only counts intact pieces 10 cm or longer, not total core recovered

Ignoring the joint orientation adjustment: it can shift the total RMR by up to 12 points and change the rock class

Using RMR alone for final support design without cross-checking against the Q-system or site-specific testing

Applying RMR derived from surface mapping directly to underground conditions without accounting for in-situ stress

Frequently Asked Questions

The Rock Mass Rating system, developed by Bieniawski in 1973 and revised in 1989, is one of the most widely used geomechanics classification systems. It evaluates six parameters to produce an RMR score from 0 to 100: uniaxial compressive strength, rock quality designation (RQD), spacing of discontinuities, condition of discontinuities, groundwater conditions, and orientation of discontinuities. Higher scores indicate better rock mass quality.

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Sources & References

Bieniawski, Z.T. (1989). Engineering Rock Mass Classifications

The primary reference for all RMR parameter ratings, class boundaries, and stand-up time correlations.

Hoek, Kaiser & Bawden (1995). Support of Underground Excavations in Hard Rock

RMR-based support design guidelines for tunnels, including rock bolt and shotcrete recommendations.

ISRM: International Society for Rock Mechanics

Standardized methods for measuring UCS, RQD, discontinuity spacing, and groundwater conditions.

Hassaan Rasheed

Developer and Researcher, CalculatorFlux

Researches and verifies the formulas, methodology, and source data behind each calculator on CalculatorFlux. All tools are built and checked against the cited references before publication.

Last updated: May 2026

RMR Classification

Score	Class
81–100	I: Very Good
61–80	II: Good
41–60	III: Fair
21–40	IV: Poor
0–20	V: Very Poor

Pro Tip

RMR should always be used alongside direct observation and professional judgment. Two rock masses with the same RMR score can behave very differently. Always pair RMR with the Q-system classification and site-specific testing for critical excavations.

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