French Drain Gravel Calculator
Estimate clean drainage-gravel volume, weight, bags and material cost for a French drain after subtracting pipe displacement.
Default project preview
7.18 yd³
Equivalent bags
402
Gross trench volume
6.67 yd³
Pipe displacement
0.259 yd³
Net gravel volume
6.41 yd³
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Drain length
Enter this project assumption in ft. The current imperial default is 80 ft.
Gravel-zone width
Enter this project assumption in in. The current imperial default is 18 in.
Gravel-zone depth
Enter this project assumption in in. The current imperial default is 18 in.
Pipe outside diameter
Enter this project assumption in in. The current imperial default is 4 in.
Settlement and handling allowance
Enter this project assumption in %. The current imperial default is 12 %. Minimum: 0. Maximum: 50.
Gravel bulk density
Enter this project assumption in tons/yd³. The current imperial default is 1.4 tons/yd³.
Bag weight
Enter this project assumption in lb. The current imperial default is 50 lb.
Price per weight unit
Enter this project assumption in per ton. The current imperial default is 58 per ton. Minimum: 0.
How to read the outputs
Equivalent bags
50 lb each. Default preview: 402.
Gross trench volume
before pipe displacement. Default preview: 6.67 yd³.
Pipe displacement
full-length cylinder. Default preview: 0.259 yd³.
Net gravel volume
before allowance. Default preview: 6.41 yd³.
Allowance
settlement and handling. Default preview: 12%.
Bulk gravel cost
at entered price per tons. Default preview: $582.78.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Net gravel volume = trench volume − pipe-cylinder volume. Order volume adds allowance; weight uses entered bulk density.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
French Drain Gravel Calculator questions
Why subtract the pipe volume?+
The pipe occupies part of the gravel envelope, reducing the aggregate volume slightly.
Should the entire trench be filled with gravel?+
Not always. The design may include soil cover, fabric folds or another surface layer.
Why can delivered weight differ?+
Moisture, gradation, compaction and supplier density change actual weight per volume.