Pro calculator
French Drain Calculator
Estimate gravel and pipe for a French drain.
How the french drain calculator works
Gravel volume = trench length × width × depth (all in ft), converted to cubic yards. Pipe length equals trench length + 10%. Fabric wraps the trench bottom and sides.
Frequently asked questions
How deep should a French drain be?
Typical residential drains are 18–24 in deep, with the perforated pipe pitched 1% (1 in per 8 ft).
Do I need filter fabric?
Yes — wrapping the trench in geotextile keeps soil out of the gravel and stops the drain from silting up.
Related calculators
All calculators
ConcreteGravelMulchTopsoilSodPaintWallpaperTileFlooringCarpetDrywallFenceDeckRoofingBTUBrickConcrete BlockMortarRebarConcrete FootingRetaining WallBlock FillBoard FootWall StudStairRafter LengthFloor JoistPlywood SheathingRoof PitchGutterMetal RoofingSnow LoadCrown MoldingBaseboardSidingWainscotingGrout & ThinsetVinyl Plank FlooringUnderlaymentBaluster SpacingDeck FastenerFurnace SizingCFMWater Heater SizingPipe VolumeWire GaugeGenerator SizingPaverGrass SeedPool VolumeFrench DrainPlant SpacingInsulationFirewood CordRamp Slope