French Drain Calculator
Calculate gravel, pipe, and materials needed for French drain installation
Calculate French Drain Materials
French Drain Configuration
Typical: 20-30 cm
Typical: 30-60 cm
Drain Pipe Details
Outside Diameter: 4.50"
Minimum Slope: 0.125%
Pipe Drop: 0.00 m
Material Requirements
Gravel Weight: 0.0 kg
Waste Included: 10%
Pipe Length: 0.00 m
Pipe Volume: 0.000 m³
Material Settings & Costs
Cost Estimation (Optional)
Example Calculation
Standard French Drain Example
Trench: 25cm wide × 30cm deep × 20m long
Pipe: 4" Schedule 40 PVC (4.5" outside diameter)
Slope: 0.125% minimum for 4" pipe
Gravel wastage: 10%
Calculation
Trench volume = 0.25 × 0.30 × 20 = 1.5 m³
Pipe length = √(20² + (20 × 0.00125)²) ≈ 20 m
Pipe volume = π × (0.057m)² × 20m = 0.205 m³
Gravel volume = 1.5 - 0.205 = 1.295 m³
With 10% waste = 1.295 × 1.1 = 1.42 m³
Result: 1.42 m³ gravel, 2 pipes (10ft each)
French Drain Components
Perforated Pipe
Collects and channels water
Holes face downward
Gravel
Filters water and supports pipe
3/4" to 1" stone recommended
Filter Fabric
Prevents soil infiltration
Geotextile material
Outlet
Where water exits system
Daylight or storm drain
Installation Tips
Maintain proper slope for drainage
Install pipe holes facing downward
Use clean, washed gravel
Wrap pipe with filter fabric
Compact soil around trench
Plan outlet location carefully
Understanding French Drains
What is a French Drain?
A French drain is an underground drainage system that consists of a trench filled with permeable materials like gravel, often with a perforated pipe at the bottom. It redirects runoff water and groundwater away from problem areas.
How Does it Work?
- •Water enters through gravel surface
- •Flows down through gravel to pipe
- •Pipe channels water to outlet
- •Prevents water accumulation
Gravel Calculation Formula
V = w × d × Lt - (π × Do²/4) × Lp
Where V = gravel volume, w = width, d = depth, Lt = trench length, Do = pipe diameter, Lp = pipe length
Pipe Slope Requirements
1/8" - 2.5" pipes: 0.25% minimum slope
3" - 6" pipes: 0.125% minimum slope
8" or larger: 0.0625% minimum slope
Important: Always face pipe holes downward and ensure continuous slope to outlet for proper drainage.