How to use this french drain gravel calculator
French-drain gravel needs can be estimated from trench volume minus the volume displaced by the drain pipe. This tool reports cubic feet, cubic yards, and approximate tons.
How the estimate works
The calculator converts trench dimensions to cubic feet, subtracts pipe-cylinder volume, adds the selected waste allowance, and converts the result to cubic yards. Estimated tons use a typical gravel density and should be confirmed with your supplier.
What the result does — and doesn’t — tell you
Use the result as a first-pass planning number. Real projects and equipment choices can change because of local prices, codes, product specifications, site access, material condition, labor, taxes, disposal fees, permitting, or engineering requirements.
- Recheck your measurements and use the actual project or equipment specifications whenever they are available.
- Compare the estimate with at least one real supplier, contractor, rental company, manufacturer chart, or local authority before committing money.
- Leave room for taxes, permits, delivery, disposal, site preparation, upgrades, or other items that are not visible in a simple online calculator.
Before you act on the result
Use the result to budget and compare supplier quotes, but measure the actual project before ordering. Material density, moisture, compaction, excavation tolerances, waste, and supplier packaging can change the delivered quantity. For bulk materials, ask the supplier what density or tons-per-yard value they use for the exact product.
Order from field measurements, not estimates alone
- Drain length (ft): Length is the biggest multiplier in trench volume and total gravel demand.
- Trench width (in): A wider trench increases gravel volume along the entire length.
- Gravel depth (in): Deeper gravel sections increase both cubic yards and delivered weight.
- Pipe diameter (in): The pipe displaces some gravel volume inside the trench.
- Waste allowance (%): A waste allowance accounts for field variation, spillage, uneven trench dimensions, and compaction.