French Drain Calculator

Calculate gravel, pipe, and filter fabric needed for a French drain. Enter trench dimensions and pipe size.

🚰 French Drain Calculator

Drain Length (ft)

Trench Width (in)

Trench Depth (in)

Pipe Diameter

Results

Gravel Needed1.6 cu yd

Gravel Weight2.2 tons

Perforated Pipe30.00 lin ft

Filter Fabric150.00 sq ft

💡 How to Calculate French Drain Materials

A French drain is a gravel-filled trench with a perforated pipe that redirects surface and groundwater away from foundations. Standard dimensions: 12 inches wide × 18 inches deep minimum. The pipe sits at the bottom on 2 inches of gravel, with gravel filling the rest of the trench.

Wrap the entire trench with landscape filter fabric before adding gravel to prevent soil from clogging the system. Use washed crushed stone (3/4 inch) — not pea gravel, which can migrate into the pipe perforations.

A 30 ft French drain, 12 inches wide × 18 inches deep: gravel ≈ 1.6 cu yd (2.2 tons). Perforated pipe: 30 lin ft. Filter fabric: about 120 sq ft.