French Drain Calculator
Estimate trench volume, drainage gravel weight, perforated pipe length, fabric rolls and material cost for a straight French drain.
Default project preview
2.75 yd³
Perforated pipe
66 ft
Fabric rolls
1
Fabric area
264 ft²
Trench volume
3.33 yd³
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Trench volume = length × width × depth. Gravel volume applies the filled percentage and allowance. Pipe length applies the same allowance; fabric width covers the bottom and both trench sides.
FAQ
French Drain Calculator questions
Should a French drain have a continuous outlet?+
Most systems need a reliable gravity outlet or engineered discharge point. A trench without an outlet can store rather than remove water.
How much slope should the pipe have?+
Required slope depends on the design and site. Use the drainage-slope calculator as a planning aid and verify the final grade.
Why is only part of the trench filled with gravel?+
Some installations include soil cover or other layers above the drainage aggregate. Enter the gravel-filled percentage for the detail being used.