What a 30 ft French drain takes
| Item | Amount |
|---|---|
| Drain rock (clean washed stone, 3/4 to 1½ in) | 1.73 cubic yards, 2.4 tons |
| Perforated pipe, 4 in | 30 ft (3 pieces of 10 ft) |
| Non-woven filter fabric | 150 sq ft |
| Soil to dig out | 1.7 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.
30 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 | 0.71 | 1.0 | 110 | 0.7 |
| 12 × 12 in | 1.12 | 1.6 | 120 | 1.1 |
| 12 × 18 in | 1.73 | 2.4 | 150 | 1.7 |
| 12 × 24 in | 2.34 | 3.3 | 180 | 2.2 |
| 18 × 24 in | 3.56 | 5.0 | 195 | 3.3 |
How deep to dig a 30 foot drain
The depth of the trench changes the stone more than anything else. For 30 ft at 12 in wide, a trench 12 in deep takes 1.1 cubic yards (1.6 tons), 18 in deep 1.7 cubic yards (2.4 tons) and 24 in deep 2.3 cubic yards (3.3 tons).
A shallow drain is enough to dry a soggy patch of lawn; a drain that has to catch water before it reaches a wall or a slab goes deeper. Dig only as deep as the water you are trying to intercept.
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 30 foot French drain?
About 1.7 cubic yards, or 2.4 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 2.3 cubic yards.
How much gravel for a 30 ft French drain 24 inches deep?
About 2.3 cubic yards (3.3 tons) at 12 in wide, against 1.7 cubic yards at 18 in deep.
How much soil comes out of a 30 ft French drain trench?
About 1.7 cubic yards for a trench 12 in wide and 18 in deep, and more once it is loose, so allow extra to haul away.
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.