Zerdly

Core Recovery Calculator

Total Core Recovery (TCR) is the length of core actually retrieved divided by the length the barrel was advanced: TCR = recovered ÷ run length × 100.

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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. Enter the drilled run length (the length advanced by the core barrel for this run) and the total length of core recovered, both in millimetres.
  2. Optionally add the solid full-diameter core length to get Solid Core Recovery (SCR), and the summed length of intact sound pieces 100 mm or longer to get RQD.
  3. Read off TCR, SCR, RQD and the rock-mass quality class; open the working panel to see each formula filled in with your numbers.

How it works

Total Core Recovery (TCR) is the length of core actually retrieved divided by the length the barrel was advanced: TCR = recovered ÷ run length × 100. Solid Core Recovery (SCR) counts only full-diameter solid cylinder: SCR = solid ÷ run length × 100. Rock Quality Designation (RQD), after Deere, is RQD = Σ(intact sound pieces ≥ 100 mm) ÷ run length × 100 — it is a directional index of intact, unweathered rock, not simply a recovery percentage.

RQD is banded into a rock-mass quality class: below 25 % Very poor, 25–50 % Poor, 50–75 % Fair, 75–90 % Good, and 90 % or above Excellent. All lengths are measured along the core axis and must share the same units, so every ratio is dimensionless and reported as a percentage. Drilling-induced fractures and mechanical breaks are re-fitted (not counted as breaks) before pieces are measured for RQD.

Worked example

A 3.0 m core run in fractured sandstone. A diamond-drilled run of 3000 mm recovers 2850 mm of core. Of that, 2400 mm comes back as solid full-diameter cylinder, and the intact sound pieces measuring 100 mm or longer add up to 2100 mm. TCR = 2850 ÷ 3000 × 100 = 95.0 %. SCR = 2400 ÷ 3000 × 100 = 80.0 %. RQD = 2100 ÷ 3000 × 100 = 70.0 %, which classifies the rock mass as Fair (50–75 %).

Common mistakes

  • Dividing recovered core by recovered core instead of by the drilled run length — RQD and TCR are always taken against the length the barrel advanced, not against what came back.
  • Counting pieces that are shorter than 100 mm, or measuring the wrong way across an angled piece — RQD uses only sound pieces 100 mm or longer measured along the core axis.
  • Including drilling-induced or handling breaks as natural fractures, which artificially lowers RQD; those breaks should be re-fitted before the pieces are measured.

Frequently asked questions

What is the difference between core recovery and RQD?

Total Core Recovery (TCR) is simply how much core came back versus how far the barrel advanced. RQD only counts intact, sound pieces 100 mm or longer, so it reflects the quality and continuity of the rock mass rather than just how much material was retrieved. A run can have 100 % recovery but a low RQD if the core is heavily fractured.

Why is the 100 mm threshold used for RQD?

Deere's original RQD definition sums the lengths of intact, sound core pieces that are at least 100 mm (4 inches) long, measured along the core axis. Pieces shorter than that, or soft/highly weathered material, are excluded because they indicate closely spaced discontinuities or poor rock. This tool uses the 100 mm convention.

Does the tool depend on the units I use?

The formulas are ratios, so any consistent unit works — but this tool asks for millimetres to match standard core-logging practice. As long as the run length, recovered length and piece lengths are all in the same unit, the resulting percentages are identical.

Can I rely on the RQD class for design?

No. The class band is a guide to rock-mass quality only. RQD feeds into wider classification systems (such as RMR or Q) and must be interpreted alongside logging, testing and a competent geotechnical professional against the relevant standard (ISRM/AS/ASTM).

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