French Drain Gravel Calculator
Estimate the drainage gravel for a French drain. Enter the trench length and width and the gravel depth around the pipe to get cubic yards and tonnes of clear stone.
French Drain Gravel Calculator Tool
How much gravel for a French drain?
A French drain is a trench filled with washed clear stone around a perforated pipe. To estimate the gravel, treat the trench as a long rectangle:
- Measure the trench length and width (often 12 inches / 30 cm wide).
- Set the depth of gravel around the pipe (commonly 8–12 inches once the pipe is bedded).
- The calculator returns the volume in cubic yards and tonnes.
Gravel volume = Length × Width × Depth
Tips
- Use washed clear stone (0–3/4" clear / 20 mm clear) with no fines so water drains freely.
- Wrap the trench and stone in landscape/filter fabric to keep soil from clogging the drain.
- Subtract the pipe volume if you want a tighter estimate, or just round up — extra stone is useful.
Frequently asked questions
How much gravel do I need for a French drain?
Multiply the trench length × width × gravel depth. A 30 ft trench, 1 ft wide with 8 inches of stone needs about 20 ft³ ≈ 0.75 cubic yards (about 1 tonne). Use the calculator for your dimensions.
What gravel is best for a French drain?
Washed clear stone (0–3/4 inch / 20 mm clear) with no fines, so water passes through freely. Avoid crusher run, which has fines that compact and reduce drainage.
How deep should a French drain be?
Typically 18–24 inches deep overall, with 8–12 inches of clear stone around a perforated pipe, sloped about 1% to carry water away.
Should I wrap the gravel in fabric?
Yes — line the trench with filter fabric so surrounding soil does not migrate into and clog the stone over time.
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Disclaimer: Results are estimates based on the values you enter and typical material densities. Actual quantities vary with gravel type, particle size, moisture and compaction. Cost estimates cover material only and exclude labour, delivery and taxes. Confirm quantities with your supplier.