French Drain Calculator
Estimate materials needed for drainage systems
Enter Dimensions
How to Use This Calculator
- Measure the length of the drainage trench needed
- Determine the width of the trench (typically 12-18 inches)
- Decide on the depth (typically 18-24 inches)
- Select the perforated pipe size (4 inch is standard)
- Click Calculate to get materials needed
Formula
French drain material calculation:
Gravel Volume (cubic yards) = (Length × Width × Depth/12) / 27
Pipe Length = Trench Length
Fabric = (Length + 4) × (Width + 2) square feet
Tips for Accurate Measurements
- Slope the trench at least 1% (1 inch per 8 feet) for proper drainage
- Use perforated pipe with holes facing down
- Wrap landscape fabric around gravel, not just line the trench
- Add a cleanout access point for maintenance
- Direct the drain outlet away from buildings
Frequently Asked Questions
What is a French drain?
A French drain is a trench filled with gravel and a perforated pipe that redirects water away from an area. It's used to prevent water accumulation and protect foundations.
How deep should a French drain be?
French drains are typically 18-24 inches deep and 12-18 inches wide. The depth depends on the water table and drainage needs.
What type of gravel should I use?
Use 3/4" to 1" crushed stone or pea gravel. Avoid sand or fine gravel as they can clog the system. Crushed stone provides better drainage.
Do I need landscape fabric?
Yes, landscape fabric prevents soil from clogging the gravel and pipe. Wrap it around the gravel, not just line the trench.
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Last updated: January 2025