How is core recovery calculated?

Divide the total measured length of recovered core by the drilled core-run length and multiply by 100. Use one consistent length unit and record the result for each run.

How is RQD calculated?

Divide the summed length of qualifying intact, hard, sound core pieces meeting the governing approximately 100 mm or 4 inch threshold by the full core-run length, then multiply by 100.

Do drilling-induced mechanical breaks reduce RQD?

They generally should not be counted like natural discontinuities. Mark and reassemble mechanical breaks under the governing procedure and project logging standard; length alone cannot establish their origin.

Can core recovery exceed 100 percent?

Yes, but it requires review. Check run limits, depth blocks, measurement, core assembly, expansion, and logging rather than silently clipping the result.

Is RQD enough for rock-mass design?

No. RQD is directional, threshold-sensitive, drilling-sensitive, and omits important discontinuity and groundwater properties. Qualified design needs the complete geologic, structural, hydrogeologic, laboratory, scale, and project context.

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Core Recovery and RQD Calculator

Core recovery and rock quality designation are run-level drill-core logging indices with different numerators and the same full drilled-run denominator. Percent recovery equals the total measured length of all recovered core divided by the run length, multiplied by 100. RQD equals the summed length of qualifying intact, hard, sound core pieces that meet the governing approximately 100 millimetre or 4 inch threshold divided by the full run length, multiplied by 100. Do not divide RQD length by recovered length. Measure every length in one consistent unit and follow the current project, agency, and laboratory procedure for the exact threshold, centreline measurement, soundness, weathering, and core-diameter rules. GeoMiner accepts millimetres, centimetres, metres, inches, or feet and displays the equivalent threshold reference. A common descriptive RQD scale labels values below 25 percent very poor, 25 to below 50 poor, 50 to below 75 fair, 75 to below 90 good, and 90 to 100 excellent. These labels describe the index only; they are not support recommendations or a complete rock-mass classification. Distinguish natural discontinuities from breaks created by drilling, core-barrel handling, transport, or logging. Mechanical breaks generally should be marked and reassembled under the governing procedure instead of automatically reducing RQD, but their origin cannot be decided from piece length alone. Recovery above 100 percent is shown rather than silently clipped because it can expose mismatched run limits, depth-block errors, core assembly problems, expansion, measurement error, or logging mistakes. Review and resolve that discrepancy before accepting the interval. Preserve the raw piece measurements and an auditable run record. RQD depends on borehole orientation, core diameter and equipment, drilling quality, recovery, threshold choice, fracture interpretation, weathering, soundness, and logging practice. It omits aperture, roughness, infill, persistence, discontinuity orientation, groundwater, stress, block geometry, and other properties that can control behaviour. Fissile, intensely weathered, or poorly recovered material can require specific treatment. Never use this calculator alone for foundations, slopes, underground support, blasting, excavation, resource estimation, or safety decisions. A defensible log records hole and run limits, depth blocks, recove

Rock mass classification guide — Understand where RQD fits inside RMR89 and Q, and where field evidence must remain separate.
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Verification resources

Cross-check terminology, classification, methods, and safety with these authoritative external resources.

undefined. Official recovery and RQD formulas, the 4-inch sound-piece threshold, treatment of mechanical breaks, and field-log context.
undefined. Core recovery and RQD logging requirements, mechanical-break handling, limitations in fissile rock, and warnings about directional dependence and joint interpretation.
undefined. RQD background, hard-and-sound core requirements, the threshold formula, common quality bands, and the directional dependence of the index.
undefined. A worked recovery and RQD example, 10.2-centimetre sound-piece threshold, quality descriptions, and drilling-quality cautions.
undefined. Current federal recommendations to use ASTM D2113 for diamond core drilling and ASTM D6032 for RQD determination.

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Common questions

How is core recovery calculated?: Divide the total measured length of recovered core by the drilled core-run length and multiply by 100. Use one consistent length unit and record the result for each run.
How is RQD calculated?: Divide the summed length of qualifying intact, hard, sound core pieces meeting the governing approximately 100 mm or 4 inch threshold by the full core-run length, then multiply by 100.
Do drilling-induced mechanical breaks reduce RQD?: They generally should not be counted like natural discontinuities. Mark and reassemble mechanical breaks under the governing procedure and project logging standard; length alone cannot establish their origin.
Can core recovery exceed 100 percent?: Yes, but it requires review. Check run limits, depth blocks, measurement, core assembly, expansion, and logging rather than silently clipping the result.
Is RQD enough for rock-mass design?: No. RQD is directional, threshold-sensitive, drilling-sensitive, and omits important discontinuity and groundwater properties. Qualified design needs the complete geologic, structural, hydrogeologic, laboratory, scale, and project context.

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Core Recovery and RQD Calculator

Connect the index to a defensible geology workflow

Verification resources

Common questions