French Drain Gravel Calculator.
Estimate the gravel volume for a rectangular French-drain trench using the dimensions you actually plan to fill. Optionally subtract the pipe volume and add your own material allowance.
Drain dimensions
Estimate the gravel volume inside a rectangular trench, with optional pipe displacement.
Enter only the depth you intend to fill with gravel.
Subtracts the cylindrical pipe volume from the gravel estimate.
Enter your own allowance for settlement, spill or site variation.
Gravel volume
Enter the drain length, trench width and gravel depth to estimate material volume.
Outputs are volume only. The calculator does not invent a gravel density or tonnage conversion because aggregate density varies by stone type, grading and moisture.
Calculate trench volume and pipe displacement
The base gravel volume is the rectangular trench length multiplied by its width and gravel-fill depth. If you enter the pipe outside diameter, the cylindrical volume of that pipe across the drain length is subtracted before any extra-material percentage is applied.
Results are shown in cubic yards and cubic metres, with cubic feet and litres as additional references. This keeps the calculation useful for both imperial and metric suppliers without using an assumed material density.
Why the calculator does not estimate tons
Two gravel products can have different bulk densities, and moisture or compaction can change weight per unit volume. Converting the result to tons without a supplier-specific density would create false precision. Use the calculated volume with the density or ordering method provided by the supplier you plan to buy from.
Frequently asked questions
How much gravel do I need for a French drain?
Enter the drain length, trench width and the depth that will actually be filled with gravel. The calculator multiplies those dimensions and can subtract pipe displacement.
Does the pipe reduce the gravel amount?
Yes, if you enter its outside diameter. The calculator subtracts the cylindrical pipe volume from the rectangular trench volume.
Why is there no tons result?
Gravel weight per cubic yard or cubic metre varies with material, grading, moisture and compaction. The tool avoids assuming a density that may not match your supplier's product.
What should I enter as extra material percentage?
Enter only the allowance you want to use for your own site conditions, settlement, spill or ordering preference. The calculator does not prefill a recommended waste percentage.