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French Drain Gravel Calculator

Estimate the cubic yards of gravel backfill needed for a French drain trench, net of the drain pipe's own volume.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax
0.33 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Gravel backfill needed

2.81 cubic yards

High confidence
Trench volume
2.71 yd³
Pipe volume (subtracted)
0.15 yd³

With the figures above, the gravel backfill needed comes to 2.81 cubic yards. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Trench volume = length x width x depth; the perforated pipe's own volume (length x pi x radius²) is subtracted since gravel doesn't fill the space the pipe itself occupies
  • 10% waste is standard for gravel to account for trench irregularities and settling

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why subtract the pipe's volume at all — isn't it small?
For a long run it adds up (over 15 m of trench, a 4 in pipe displaces over a tenth of a cubic yard) — subtracting it avoids over-ordering gravel.
Should I use washed gravel or any gravel?
Use clean, washed drainage gravel (often 3/4 in or larger) without fines — gravel with sand or dust content clogs the perforations and defeats the drain's purpose over time.
Does this include the fabric sock or filter fabric?
No — this is gravel volume only. Filter fabric to wrap the trench (preventing soil migration into the gravel) is estimated separately by trench surface area.