🌧️ French Drain Calculator
Estimate how much gravel and perforated pipe you need to build a French drain, based on your trench dimensions.
What this calculator does
The French drain calculator estimates how much gravel and perforated pipe you’ll need to build a drainage trench that redirects water away from a foundation or low spot.
The formula
The calculator converts your trench length, width, and depth to feet and multiplies them to find total volume, then converts cubic feet to cubic yards (dividing by 27) since gravel is usually sold by the cubic yard or by weight. An approximate weight is also shown using a typical gravel density of about 1.4 tons per cubic yard. The length of perforated pipe needed equals the trench length.
This tool is for general planning purposes. Always follow local codes for drain slope (typically a minimum of 1% grade), pipe sizing, and an outlet or dry well location.