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French Drain Material Calculator
Updated Aug 25, 2026 Reviewed Aug 25, 2026
Estimate excavation, gravel, pipe stock, couplers, slope fall, filter fabric and optional cost for multiple drain runs.
Drainage material takeoff
Enter trench runs, gravel envelope, pipe and fabric
Result
Calculation summary
Enter values to see the result
Your result, breakdown, assumptions, and warnings will appear here.
Drain preview
Gravel envelope and sloped profile
Drain runs
1
Order gravel
3.368 m³
Pipe stock pieces
5
How to use this calculator
- 1Add each straight drain run.
- 2Enter trench and gravel-envelope dimensions plus pipe outside diameter.
- 3Choose fabric layout and pipe stock length.
- 4Set gravel density, waste, output units and optional prices.
Formula
Net gravel = gross gravel envelope − pipe displacement
Full excavation, fabric wrap, pipe stock and slope fall are calculated independently.
Calculation steps
- Calculate excavation.
- Subtract pipe displacement from gravel.
- Apply gravel waste and density.
- Round pipe stock and count couplers.
- Calculate fabric and slope fall.
Worked example
A 10 m by 1 m by 0.5 m gravel envelope with one 100 mm pipe holds about 4.921 m³ before waste.
Assumptions
- This is not drainage design.
- Pipe is fully inside the gravel envelope.
- Fabric uses a rectangular envelope.
- Entered slope is not approved by the tool.
- Costs exclude excavation, labor, delivery and tax.
Sources
Frequently asked questions
Why subtract pipe volume?
The pipe occupies space that cannot contain gravel.
Why separate trench and gravel depth?
Excavation and the gravel envelope may differ.
Does it choose slope?
No. It only reports fall from your entered slope.
Are bends included?
No. Only intermediate stock-length couplers are counted.
How is filter fabric estimated?
Choose a U lining or full rectangular wrap; seam overlap is added once across the run.
Does the result verify the outlet?
No. Outlet elevation, discharge conditions and hydraulic capacity must be checked separately.
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