EstimatorPad

French Drain Calculator

Turn an already planned gravel-filled French drain into a transparent material takeoff. Subtract the pipe’s outside volume from the stone envelope and calculate pipe stock and fabric wrap separately.

Enter measurements below. Results update as you type, and optional prices can be added before sharing the estimate.

MEASURED MATERIAL TAKEOFF

Estimate french drain quantities

Use measured dimensions and the exact product or supplier values. The starting measurements are a worked example.

ft
in
in

Only the gravel-filled depth; exclude topsoil or other backfill.

in

Use actual outside diameter; enter 0 for a stone-only trench.

ft
in

Allowance across the top wrap; use the specified fabric detail.

USD/yd³
%

Local calculations. No signup required.

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The calculation

French Drain Calculator method

Stone volume = length × (width × stone depth − π × outside pipe diameter² ÷ 4); fabric width = 2 × width + 2 × stone depth + overlap

  • Use the gravel-filled envelope depth, excluding topsoil or other backfill. The tool does not calculate total excavation.
  • Pipe displacement uses the outside diameter, not the nominal inside bore. Enter zero for a stone-only trench.
  • Pipe sections are rounded separately; stone waste does not increase pipe length. Fabric output is a cut-width/area takeoff, not a whole-roll layout.
  • The wrapped rectangle includes bottom, sides and top plus the specified overlap. End closures, longitudinal roll seams, fittings and outlets need separate allowances.
  • This is not a pipe capacity or drainage design calculator. Confirm slope, depth, outlet, soil, utility clearances and system compatibility before construction. It is not for gravel-free bundles.

Quick examples

50 ft run; 12 in wide × 18 in stone envelope75 cu ft before pipe displacement
4 in pipe outside diameter; 10% stone allowanceAbout 2.878 cu yd of gravel
10 ft pipe sections; 12 in wrap overlap5 pipe sections; 6 ft fabric cut width; 300 sq ft wrap area

Examples are planning checks. Product-label coverage and whole pack sizes control the final purchase quantity.

Verified references

Check the exact product data before ordering

NDS definitive drainage guide

Manufacturer drainage planning reference; system sizing and installation are separate from this material takeoff.

Open source

NDS French drain systems

Shows why proprietary gravel-free systems require different quantities.

Open source

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Common questions

Understand the result before purchasing

01How much gravel does a French drain need?+

Multiply the gravel-filled width and depth by run length, subtract the outside pipe cylinder, then add your material allowance.

02Do I enter the full trench depth?+

Enter only the depth filled with drainage stone. Topsoil or other non-stone backfill must be excluded.

03What pipe diameter should I use?+

Use the actual outside diameter from the pipe specification. This determines displaced stone volume; the calculator does not determine the required pipe flow capacity.

04How is the filter fabric quantity calculated?+

The fabric wraps the bottom, both sides and top of the rectangular stone envelope, plus the entered overlap. Multiply that cut width by run length. End closures and roll seams are additional.

05Can I use this for gravel-free drain products?+

No. Gravel-free bundles and proprietary systems require their manufacturer’s own quantities and installation instructions.