Material logic
Gravel volume = trench length x trench width x gravel depth, plus extra material. Pipe length is roughly the trench run.
RainYard Tools
Trench material
French Drain Gravel Calculator
Estimate gravel, fabric, and pipe length for a French drain trench.
Before you calculate
Use it as a gravel calculator for a French drain after the trench size and outlet are settled.
- French drains move water, they do not make water disappear.
- A trench still needs an outlet.
- Do not pipe roof water into a foundation problem.
Gravel5.50 cu ydOrder volume before supplier rounding.
Pipe length60 ftAdd fittings and cleanouts separately.
Fabric width6.0 ftRough wrap width around the trench.
1
Measure the trench run.
2
Enter gravel width and depth.
3
Add extra for uneven excavation.
Example
A 60 ft trench that is 1.5 ft wide and 1.5 ft deep needs about 5.5 cubic yards of gravel after a 10% extra allowance.
A French drain must discharge somewhere
The trench collects and moves water. It still needs daylight, a dry well, a storm connection where allowed, or another legal outlet.
Avoid the wrong fix
If water is coming from roof downspouts, start by extending or capturing roof water before trenching the yard.
Use the material page after sizing the trench
If you still need to decide whether the trench is big enough for the storm, go back to the French drain calculator first. Then return here to order stone and fabric.
Questions
Common checks.
Does fabric count in the gravel estimate?
No. The calculator estimates a rough fabric wrap width separately.
Can I make the trench narrower?
A narrow trench may work for some jobs, but it stores less water and is harder to maintain.
Should pipe be perforated?
Most French drains use perforated pipe in gravel, but outlet and soil conditions matter.