French Drain Calculator
Calculate all materials needed for a French drain installation — drainage gravel, perforated pipe, landscape fabric, and trench excavation volume. Enter your drain length and trench dimensions for a complete material list.
Enter Trench Dimensions
Full Material List
Trench Volume
Gravel Needed
Gravel Weight
Perforated Pipe
Landscape Fabric
Pipe Sock / Sleeve
Gravel Cost
How to Use This Calculator
- Enter the total length of your French drain run.
- Select trench width — 12" is standard for residential drains.
- Select trench depth — 18" minimum; deeper for more capacity.
- Choose your pipe diameter — 4" is standard residential.
- Optionally enter a gravel price for cost estimates.
The Formula
Trench Volume (cu ft) = Length × (Width/12) × (Depth/12)
Gravel Volume (cu yd) = Trench Volume ÷ 27
Gravel Weight (tons) = Cubic Yards × 1.4
Washed drainage gravel (#57 stone) weighs approximately 2,800 lbs (1.4 tons) per cubic yard. The pipe displaces a small amount of gravel volume, but we keep the full trench volume to ensure adequate drainage capacity.
Fabric = (2 × Depth + Width + 12") × Length
Landscape fabric lines the trench bottom and sides with 6" overlap at top.