Calculate exactly how much gravel, pipe, and fabric you need for your French drain. Professional drainage estimates in seconds.
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Enter your trench dimensions
Small landscape areas
Under 300 sq ft
Standard residential
300-1000 sq ft
Large or heavy flow
Over 1000 sq ft
Note: 4-inch perforated pipe is standard for most residential applications. Upgrade to 6-inch for areas with heavy water flow or when draining large surfaces.
Why expert review matters
Every calculator is reviewed by certified professionals to ensure accuracy.David Chen's Master Mason, Licensed GC certification ensures professional-grade precision.
How deep should a French drain be?
18-24 inches is ideal. Minimum 12", but deeper is better for drainage and freeze protection.
What type of gravel should I use?
3/4" washed stone or pea gravel. Avoid crushed limestone - it compacts and clogs.
How much slope does it need?
Minimum 1% slope (1" per 10 ft). 2% slope is better for optimal flow.
Holes up or down on the pipe?
Holes facing DOWN collects groundwater better. Holes up only for surface water.
Our French drain calculator determines the exact amount of gravel, perforated pipe, and landscape fabric needed for your drainage project. The calculator accounts for pipe displacement (gravel volume reduced by pipe size) and uses the wrap method for fabric calculation to ensure complete trench coverage.
Gravel Formula
Volume = (Length × Width × Depth) × (1 - Pipe Displacement %)
Convert to cubic yards: Volume ÷ 27
Fabric Formula
Sq Ft = Length × (Width + 2 × Depth)
Covers trench bottom + both sides
Mark drain path with spray paint. Dig trench 12-24" deep with 1-2% slope.
Line trench bottom and sides with landscape fabric, leaving extra for wrap.
Add 2-3" of gravel base. Ensure proper slope with level or laser.
Place perforated pipe holes-down. Connect sections with couplers.
Cover pipe with gravel to 2-4" below ground level. Maintain slope.
Fold fabric over gravel. Top with soil or decorative stone.