What a 100 ft French drain takes
| Item | Amount |
|---|---|
| Drain rock (clean washed stone, 3/4 to 1½ in) | 5.76 cubic yards, 8.1 tons |
| Perforated pipe, 4 in | 100 ft (10 pieces of 10 ft) |
| Non-woven filter fabric | 500 sq ft |
| Soil to dig out | 5.6 cubic yards |
For a trench 12 in wide and 18 in deep, with 10% extra stone for uneven trench walls and settling. The stone is the trench volume less the space the pipe takes up, at 1.4 tons per cubic yard.
100 ft of drain, by trench size
Width × depth of the trench, with a 4 in pipe and 10% extra stone.
| Trench | Drain rock, cubic yards | Tons | Fabric, sq ft | Soil dug out, cubic yards |
|---|---|---|---|---|
| 8 × 12 in | 2.36 | 3.3 | 367 | 2.5 |
| 12 × 12 in | 3.72 | 5.2 | 400 | 3.7 |
| 12 × 18 in | 5.76 | 8.1 | 500 | 5.6 |
| 12 × 24 in | 7.79 | 10.9 | 600 | 7.4 |
| 18 × 24 in | 11.87 | 16.6 | 650 | 11.1 |
Ordering stone for 100 feet
At 100 ft the stone is a truck delivery: 5.8 cubic yards, 8.1 tons, with the usual 10% extra. With a careful, straight-sided trench and 5% extra it is 7.7 tons; with ragged walls in stony ground, allow 15% and order 8.4 tons.
Ask the supplier how much one truck carries and where it can tip. Stone dumped at the far end of a 100 ft trench has to be moved by wheelbarrow, so have it tipped as close to the middle of the run as the truck can reach.
Use clean, washed stone with no fines, wrap the stone (not the pipe) in the fabric, and make sure the drain has an outlet. The fittings, tools and steps are in the French drain materials list, and the method behind the stone figure is in how much gravel for a French drain.
Want to change anything else? The calculator above is the full French Drain Calculator: edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
How much gravel do I need for a 100 foot French drain?
About 5.8 cubic yards, or 8.1 tons, of clean drain rock for a trench 12 in wide and 18 in deep with a 4 in pipe, including 10% extra. A 12 by 24 in trench takes 7.8 cubic yards.
How many yards of gravel for a 100 ft French drain?
About 5.8 cubic yards (8.1 tons) for a 12 by 18 in trench, and 7.8 cubic yards if it is 24 in deep.
How much extra gravel should I order?
About 10% for an ordinary hand-dug trench. For 100 ft that is 8.1 tons, against 7.7 tons at 5% and 8.4 tons at 15%.
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.