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French drain cost calculator

Length, depth and width give the trench volume and the fall. Your rates give the price.

A French drain cost calculator starts with the trench: length, depth and width set the volume of gravel and the fall the pipe needs.

This tool works out cubic yards and how much lower the far end sits at a 1/8 inch per foot slope, then prices labor and gravel only at rates you type from a quote. It contains no prices of its own.

French drain calculator

Length, depth and width give the trench volume and the fall. Your rates give the price.

From a written quote. No default: we hold no price data.

Only if you buy gravel separately.

— Price at your rates
— Trench volume
— Fall over the run
— Before you dig

What this assumed —

Geometry is ours; prices are yours. Not a drainage design.

The outlet matters more than the length

A French drain is a gravel trench with a perforated pipe that moves water by gravity. It only works if the pipe falls the whole way and ends somewhere lower: daylight, a dry well or a legal storm connection. A long drain with nowhere to go is a buried pond.

Foundation drains are a code item. IRC R405 requires drains around concrete or masonry foundations that retain earth and enclose space below grade, with gravel at least 1 foot beyond the footing and 6 inches above it. That is different from a yard drain. See basement waterproofing.

Call 811 before you dig. Buried utilities run where drains want to go.

Questions this calculator answers

How much gravel does a French drain need?
Length × depth × width, less the pipe. A 50 ft trench 18 in deep and 12 in wide is about 2.8 cubic yards. The calculator does this for your numbers.
How much slope does a French drain need?
The tool illustrates 1/8 inch per foot, a common minimum for drain pipe. Your designer or local code sets the actual slope. Steeper is usually safer for a drain that must clear silt.
Why no cost per foot?
We hold no sourced, dated price data for French drains. Enter the installed rate from your quote. Access, depth, soil and the outlet change it more than length.
Can a French drain fix a wet basement?
Sometimes, if the water comes through the soil at the wall. If it comes from roof runoff, gutters and downspout extensions are cheaper and come first.

Sources and methodology

Figures dated 26 October 2026. Last reviewed .

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