Use this Rock Mass Rating Calculator to get an instant RMR score and rock class (I–V). It’s free to use, easy to understand, and built for quick field or desk work.
Rock Mass Rating (RMR) Calculator
Enter the scores for each parameter (no ranges). Click Calculate.
What is the Rock Mass Rating?
RMR (Rock Mass Rating) is a common method for evaluating and measuring the quality of rock at a site. It was created by Bieniawski (1989), and Engineers use it in tunneling, mining, foundations, and slope design.
RMR combines six properties into a single number, ranging from 0 to 100. Higher numbers mean better rock. So if RMR is high, near 100, it means the rock is better. Below, I have explained everything in detail.
Rock Mass Rating Calculation Formula
RMR formula consists of six parts:
- Intact rock strength (σci): 0–15
- RQD (Rock Quality Designation): 0–20
- Discontinuity (joint) spacing: 0–20
- Condition of discontinuities: 0–30
- Groundwater condition: 0–15
- Orientation adjustment: 0 to −12 (0 if favorable; negative if unfavorable)
The formula for the rock mass rating is the sum of all the above factors. Which is
RMR = strength + RQD + spacing + condition + groundwater + orientation
- Intact rock strength (σci): How strong are the rock pieces by themselves. Stronger rock = higher score.
- Discontinuity (joint) spacing: How far apart the cracks/joints are. Bigger gaps between joints = higher score.
- Condition of discontinuities: How “good” the joints are: rough or smooth, clean or filled, fresh or weathered, tight or open. Rough, clean, tight joints = higher score; smooth, soft-filled, weathered, open joints = lower score.
- Groundwater condition: How wet the rock mass is. Dry or slightly damp = higher score; dripping, flowing, or high-pressure water = lower score.
- Orientation adjustment: How the joint directions line up with your tunnel/slope/foundation. Favorable = 0 (no penalty). Unfavorable = subtract points (down to –12).
How to Calculate Rock Mass Rating (step-by-step)
- Score each input (strength, RQD, spacing, condition, groundwater).
- Set orientation to 0 if joint orientation is favorable; use a negative value (down to −12) if it’s unfavorable.
- Add all six values and click on the calculate button to get the Total RMR.
- Match the score to the rock class using the chart below.
Rock Mass Rating Calculation Example
Let’s say your scores for each factor are:
- Strength: 12
- RQD: 14
- Spacing: 12
- Condition: 12
- Groundwater: 12
- Orientation: −2
RMR = 12 + 14 + 12 + 12 + 12 − 2 = 60
Class = III (Fair rock)
Rock Mass Rating Chart
| Class | RMR Range | Description |
| I | 81–100 | Very Good rock |
| II | 61–80 | Good rock |
| III | 41–60 | Fair rock |
| IV | 21–40 | Poor rock |
| V | ≤ 20 | Very Poor rock |
Our calculator will show you the Class and Description based on RMR Range after you click on the calculate button as you can see in below screen shot.
Final Notes
This RMR is based on the Bieniawski system. Your numbers should come from your project’s standard tables for strength, RQD, spacing, joint condition, groundwater, and orientation.
If you found this rock mass rating calculator useful, bookmark the page and share it with your team.