Home / Science / Earth sciences / Mining and economic geology / Rock mass classification (Q, RMR, RQD)Tool #514

Rock mass classification calculator: RQD from core, Q-system, RMR sum, RMR–Q correlation and GSI estimate

Work out RQD from core piece lengths (Deere), Barton's Q = (RQD/Jn)(Jr/Ja)(Jw/SRF) and Bieniawski's RMR as a sum of the ratings you read from the published tables, then compare them with an editable RMR = A ln Q + B correlation and get GSI estimates. Arithmetic only: no rating tables are bundled.

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  1. Core pieces
  2. Q and RMR
  3. Correlate
  4. Report
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Arithmetic only. Read every rating and parameter from the published tables (Barton, Lien and Lunde 1974 and later updates for Q; Bieniawski 1989 for RMR). This page does not hold those tables and is not a design.

RQD from a core run

Deere's RQD: the total length of sound core pieces 10 cm or longer, as a percentage of the run length. Measure along the core's centre line, count only natural breaks (not breaks from drilling or handling), and leave out pieces that are soft or badly weathered. The example is made up.

Q-system

RMR (sum of ratings)

Type the ratings from Bieniawski's (1989) tables. The example ratings are made up.

RMR–Q correlation and GSI

A = 9, B = 44 is Bieniawski's (1976) widely used fit; other studies found other values for their rock (the scatter is large), so change A and B to suit. GSI estimates: GSI ≈ RMR89 with dry groundwater and no adjustment, minus 5 (Hoek, Kaiser and Bawden 1995, for RMR above 23), and GSI ≈ A ln Q′ + B with Q′ = (RQD/Jn)(Jr/Ja). Check GSI against the Hoek–Marinos chart in the field.

Data
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What it does

Rock mass classifications put numbers on how blocky, rough, weathered, wet and stressed a rock mass is. This page does the arithmetic for the three most used ones, with ratings that you read from the published tables:

  • RQD from a core run (Deere): type the run length and the lengths of the core pieces in order. The page adds up the sound pieces 10 cm or longer (you can change the cut-off), gives RQD as a percentage of the run, the core recovery, and a drawing of the run with counted pieces dark, short ones light and lost core dashed.
  • Q-system (Barton and others): Q = (RQD/Jn) × (Jr/Ja) × (Jw/SRF). The three quotients stand for relative block size, shear strength between blocks and active stress. RQD can come from the core run or be typed; below 10 it is taken as 10, as Barton advises (you can switch that off). Q′ (without the water and stress terms) is shown too.
  • RMR (Bieniawski 1989): the sum of five ratings (intact rock strength, RQD, joint spacing, joint condition, groundwater) plus an orientation adjustment that is zero or negative.
  • Correlation and GSI: RMR = A ln Q + B with A and B you can change (Bieniawski’s 9 and 44 to start), both ways, with a chart; GSI ≈ RMR89 with dry groundwater − 5, and GSI ≈ A ln Q′ + B.

The rating tables are not included. Each input has a one-line reminder of what it describes; take the value from the original papers or a rock mechanics textbook. This page is arithmetic, not a design.

How to use it

  1. Type the core run length and the piece lengths (commas, spaces or new lines). Measure along the centre line and leave out breaks made by drilling.
  2. Type Jn, Jr, Ja, Jw and SRF from the Q tables.
  3. Type the five RMR ratings and the orientation adjustment from the RMR tables.
  4. Compare: if RMR and Q disagree a lot, recheck the ratings, or fit your own A and B for the site.
  5. Download a CSV of the results, or a PNG, PDF or Word report.

Worked example (made-up numbers)

A 150 cm run with pieces 25, 8, 12, 4, 30, 6, 18, 9, 11, 3 and 14 cm: six pieces are 10 cm or longer, 110 cm in all, so RQD = 73.3 %; the 140 cm of core is a 93.3 % recovery.

With Jn = 9, Jr = 1.5, Ja = 2, Jw = 1 and SRF = 1: RQD/Jn = 8.15, Jr/Ja = 0.75, Jw/SRF = 1, so Q = 6.11.

Made-up RMR ratings 7 + 13 + 10 + 20 + 10 = 60, with a −5 orientation adjustment: RMR = 55. The correlation gives RMR 60.3 from Q (5.3 more than measured) and Q 3.39 from RMR. GSI from RMR89 (groundwater set to 15, dry) is 60, and from Q′ about 60.3.

Tips

  • Log RQD for each run, not each hole: one average hides weak zones.
  • Q spans about 0.001 to 1000, so compare it on a log scale.
  • The RMR–Q correlations scatter widely; treat them as a check, not a conversion.

FAQ

Why are there no rating tables? The tables belong to their authors’ publications; please use them from the source. The page checks only simple limits (RQD 0 to 100 %, Jw at most 1, RMR at most 100).

Can I use RQD from a scanline or Jv? Yes: switch “RQD from” to a typed value.

Where the numbers come from

  • Deere (1964), Deere and Deere (1988): rock quality designation, RQD = sum of sound core pieces 10 cm or longer ÷ run length × 100 (definition only).
  • Barton, Lien and Lunde (1974), Engineering classification of rock masses for the design of tunnel support, Rock Mechanics 6: the Q formula (the rating tables are not reproduced; use the published tables).
  • Bieniawski (1989), Engineering Rock Mass Classifications, Wiley: RMR as the sum of five ratings and an orientation adjustment (tables not reproduced). Bieniawski (1976) for the correlation RMR = 9 ln Q + 44.
  • Hoek, Kaiser and Bawden (1995), Support of Underground Excavations in Hard Rock: GSI ≈ RMR89′ − 5 and GSI ≈ 9 ln Q′ + 44.
  • Example core run and ratings made up by fibub.

Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.

Last updated 2026-11-09.

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