French Drain Calculator
Find gravel for a French drain trench.
Estimate the gravel to fill a French drain trench.
How the Math Works
The French Drain Calculator uses the formula yd³ = length × width × depth ÷ 27 to determine gravel volume. This formula first calculates the trench volume in cubic feet by multiplying its length, width, and depth. Since gravel is sold by the cubic yard, dividing by 27 converts cubic feet to cubic yards (since 1 cubic yard = 27 cubic feet). This ensures accurate material estimates for your drainage project.
Practical Applications
To apply this calculation, measure your trench's dimensions: length in feet, width (typically 1-1.5 feet), and depth (usually 1-3 feet). Input these values into the calculator. For example, a 20-foot-long trench with 1-foot width and 2-foot depth requires (20×1×2)÷27 ≈ 1.48 cubic yards of gravel. Always round up to the nearest half-yard to account for settling or uneven trenches.
Day-to-Day Use
This tool simplifies solving everyday water drainage problems, preventing basement flooding, soggy lawns, or soil erosion. By calculating precise gravel needs, you avoid overbuying materials, saving time and money. It’s invaluable for homeowners tackling DIY drainage projects, ensuring efficient water flow away from foundations, gardens, or low-lying areas without costly professional help.
Worked example
50 × 1 × 2 ft → 3.7 yd³.
FAQ
Pipe space?
The perforated pipe displaces a little gravel — this gives a safe estimate.