French Drain Calculator

Estimate gravel, pipe, and filter fabric requirements for a professional-grade French drain system.

Trench Dimensions

Unit System

Trench Length (ft)

Trench Width (in)

Trench Depth (in)

Materials Estimate

Solving drainage issues?

Enter the dimensions of your trench to determine the total materials required for an effective drainage solution.

Overview

A French drain is a gravel-filled trench containing a perforated pipe that redirects surface and groundwater away from a structure's foundation. It is one of the most effective ways to prevent basement flooding and eliminate standing water in yards. Proper wrapping with filter fabric is critical to prevent soil from clogging the gravel core.

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Pro Tips

Use 3/4" to 1-1/2" washed drainage rock (no sand or fines) to maximize water flow and prevent the system from silting up.
Ensure the exit point (daylight) of the pipe is protected from debris and rodents with a grated cap or dry well.
Before digging, call your local utility locator service (e.g., 811 in the US) to avoid hitting underground gas or water lines.

Fun Facts

"The French drain was named after Henry Flagg French, an American lawyer and judge, who popularized the design in 1859."
"A minimum slope of 1% (roughly 1 inch of drop per 8 feet of length) is essential for water to move effectively by gravity."
"Always place the perforated pipe with the holes facing DOWN into the gravel bed to allow water to rise into the pipe and flow away."

Formula: Volume = (Length × Width/12 × Depth/12) / 27; Fabric = Length × (2 × Depth/12 + 2 × Width/12)

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