Project Hub

Drainage Project Hub

French drain, drainage gravel, and slope planning calculators for yard water problems. Every calculator returns trench volume, gravel tons, pipe length, and required drop across the run.

Yard drainage projects almost always come down to three numbers: how long the trench is, how deep it needs to be to hit daylight, and how much washed drainage stone to order. Get any of them wrong and the drain either fails to move water or costs a second delivery to finish. This hub groups the french drain calculators with the reference guides that answer the sizing questions before you dig.

Start with the french drain calculator for trench volume and pipe length, then use the slope calculator to confirm the outlet is low enough, and the cost calculator to compare bulk gravel to bagged.

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French Drain Calculator

Trench volume, drainage gravel, and perforated pipe length for a french drain run.

Calculators

CalculatorFrench Drain CalculatorTrench volume, gravel, and pipe length.CalculatorFrench Drain Slope CalculatorRequired drop from start to outlet at 1 percent minimum grade.CalculatorFrench Drain Cost CalculatorBulk vs bagged stone, pipe, and fabric cost estimate.CalculatorDrainage Gravel CalculatorCubic yards and tons of washed drainage stone.CalculatorCrushed Stone CalculatorGeneral crushed stone volume for any drainage lift.

Planning and reference guides

GuideHow Much Gravel for a French Drain?GuideFrench Drain Slope Guide GuideFrench Drain Pipe Size Guide GuideFrench Drain vs Swale

Common questions

How much slope does a french drain need?: At least 1 percent, or 1 inch of drop per 10 feet of pipe. Steeper is fine; flatter risks standing water in the pipe.
What size gravel goes in a french drain?: Washed 3/4 to 1 1/2 inch drainage stone. Avoid gravel with fines, which clog the perforations.
How deep should a french drain trench be?: 12 to 18 inches for surface water, 24 to 36 inches for foundation drainage. The outlet must be lower than the trench bottom to maintain slope.

Related project hubs

Landscaping Materials

Gravel, mulch, topsoil, and river rock sizing.

Concrete Project Hub

Cubic yards, bags, and slab thickness for a pour.

Landscaping Calculators

All landscaping tools.

Sources and methodology

Trench volume uses length x width x depth in feet, converted to cubic yards. Slope defaults to a 1 percent minimum per USDA NRCS surface drainage guidance. Gravel weight uses 100 lb per cubic foot for washed drainage stone. See our full methodology page for how we source and review each figure.

Last reviewed January 15, 2026.