/// Short answer
stone for a French drain — the planning answer
Estimate stone for a French drain by measuring the trench envelope, subtracting the pipe displacement when appropriate, and calculating each trench section separately. Convert the remaining volume to cubic yards or tons using the exact drainage-stone density from the supplier. Fabric, pipe, fittings, outlets, and excavation are separate scope items. The quantity calculation does not design the drain slope or discharge path.
How do you estimate stone for a french drain?
Estimate stone for a French drain by measuring the trench envelope, subtracting the pipe displacement when appropriate, and calculating each trench section separately. Convert the remaining volume to cubic yards or tons using the exact drainage-stone density from the supplier. Fabric, pipe, fittings, outlets, and excavation are separate scope items. The quantity calculation does not design the drain slope or discharge path.
Stone volume = trench volume − pipe displacement − other measured voids. Weight uses the supplier's product density, not a universal stone conversion.
/// Continue with the numbers
Run the stone calculator
Use the stone calculator to combine separate rectangular or circular areas into a transparent bulk volume. Weight remains optional until you enter the selected stone's supplier density, preventing one material from standing in for another. Review each area's depth, add a job-specific allowance, and use the resulting cubic yards when discussing delivery.
/// Keep the topic connected
Related calculators
Use the neighboring tools to keep each material, layer, and order assumption visible instead of hiding it inside one estimate.
What should you measure first?
Record trench length, width, stone depth above and below the pipe, pipe outside diameter, cleanouts, and changes in section. Keep imported stone separate from excavated material.
- Measure each trench section and its stone envelope.
- Record pipe outside diameter and any larger chambers.
- Identify clean stone size, density, delivery unit, and fabric overlap separately.
What should you verify before ordering?
Drainage performance depends on slope, soil, filter fabric, pipe, outlet, groundwater, and site grading. Verify the design before excavation or material ordering.
- Check whether the supplier sells by ton, yard, or bag.
- Subtract pipe displacement only when it is included in the measured envelope.
- Confirm outlet and access conditions with the project plan.
/// Continue the workflow
Related ProjectQty pages
/// Field-ready worksheet
Download the measurement checklist
Use the worksheet to record dimensions, product-label values, and verification notes locally. ProjectQty does not receive or store your project inputs.
/// Evidence trail
Sources and assumptions
This article inherits the calculator's declared source scope. Product yields, coverage, density, and label rates should be replaced with the exact product selected for the job.
Exact international-foot to meter conversion; U.S. survey-foot conversion is explicitly outside this claim.
NOAA National Geodetic Survey · Prequalified fallbackThe DSDATA Format, Appendix D: U.S. Survey Foot vs International FootIndependent confirmation that one international foot equals exactly 0.3048 meters; U.S. survey-foot conversion remains distinct.
National Institute of Standards and Technology · Primary evidenceNIST Handbook 44 (2026): exact avoirdupois pound to kilogram conversionExact international avoirdupois-pound conversion; troy and apothecaries pounds are excluded.
The National Archives (UK Legislation) · Prequalified fallbackWeights and Measures Act 1985, section 1: pound definitionIndependent statutory confirmation of the exact international avoirdupois-pound definition.
National Institute of Standards and Technology · Primary evidenceNIST Handbook 44 (2026): exact U.S. short-ton definitionExact U.S. short-ton definition; long ton and metric tonne are excluded.
North Carolina General Assembly · Prequalified fallbackNorth Carolina General Statutes: short-ton definitionIndependent statutory confirmation that the U.S. short ton is 2,000 avoirdupois pounds.
/// Common questions
How Much Stone Do You Need for a French Drain? FAQ
Do I subtract the drain pipe from the stone volume?
Subtract the pipe displacement when the trench dimensions describe the full stone-filled envelope. If your measured area already excludes the pipe, do not subtract it twice.
What density should I use for drainage stone?
Use the supplier's value for the exact size and product. Voids, grading, and moisture make universal tons-per-yard shortcuts unreliable.
Does this calculate French drain slope?
No. It estimates fill volume from entered geometry. Slope, outlet, groundwater, fabric, and pipe design require site-specific review.