French Drain Materials List: Gravel, Pipe, Fabric and Tools
A 50 ft French drain in a trench 12 inches wide and 18 inches deep takes about 2.9 cubic yards (4.0 tons) of washed stone, 50 ft of perforated pipe, 250 ft² of filter fabric, and you will dig out about 2.8 cubic yards of soil. Here is the full list and how to build it so it actually drains.
The materials list
| What to buy | How much | How we worked it out |
|---|---|---|
| Washed drainage stone | 2.9 yd³ (4.0 tons) | French drain calculator: the trench volume less the pipe, plus 10%. Use clean, angular stone of 3/4 to 1½ in, with no fines |
| Perforated pipe (4 in) | 50 ft, or five 10 ft pieces | A rigid or flexible perforated drain pipe. Order a solid pipe for the section that carries water out to the discharge point |
| Non-woven filter fabric | About 250 ft² | Lines the trench and wraps over the top of the stone, with overlap, so that soil cannot wash in and clog it |
| Pipe fittings | Couplers, an elbow and an end cap | To join the lengths and finish the end |
| Pop-up drain or outlet | 1 | Where the water comes out: a daylight exit downhill, a dry well or a storm drain, where allowed |
| Topping | A few inches of soil, sod or decorative stone | To finish the surface |
| Tools | Trenching shovel, wheelbarrow, level or string, tamping tool | A rented trencher saves time on long runs |
A wider and deeper trench holds more stone: at 18 inches wide and 24 inches deep, the same 50 ft takes 5.9 cubic yards.
Materials for other lengths
Trench 12 in wide and 18 in deep, 4 in pipe, 10% extra stone:
| Drain length | Drain rock | Pipe (10 ft pieces) | Filter fabric |
|---|---|---|---|
| 25 ft | 1.4 yd³ (2.0 tons) | 3 | 125 ft² |
| 50 ft | 2.9 yd³ (4.0 tons) | 5 | 250 ft² |
| 75 ft | 4.3 yd³ (6.0 tons) | 8 | 375 ft² |
| 100 ft | 5.8 yd³ (8.1 tons) | 10 | 500 ft² |
What makes it work
- Slope. Water only flows downhill. Aim for a fall of at least 1 inch for every 8 feet of drain, all the way to an outlet.
- Clean stone. Sand and crusher run have fines that clog the drain. Use washed stone.
- Fabric. Wrap the stone, not the pipe, in non-woven geotextile, so water gets in but soil stays out.
- An outlet. A drain with nowhere to discharge just fills up. Keep the outlet clear and away from your foundation, your septic area and your neighbors' property.
- Where it goes. A drain should intercept the water before it reaches the problem area, and run away from the house.
How the job goes
- Call 811, mark the line, and check the slope with a string and a level.
- Dig the trench to the planned depth with a constant slope. Plan to haul away about a quarter more soil than the trench volume, because soil expands when dug.
- Line the trench with filter fabric, leaving enough on each side to fold over the top.
- Put 2 to 3 inches of stone in the bottom, lay the pipe on it with the holes down, check the slope, and add stone to the top of the pipe and beyond.
- Fold the fabric over the stone, cover with a few inches of soil, sod or decorative stone, and test it with a hose.
A drain deals with groundwater and runoff, but it is not a substitute for guttering that sends roof water well away from the house. For stone weights and ordering, see the gravel tons guide. Estimates only: serious drainage problems near a foundation deserve a professional.
Frequently asked questions
How much gravel do I need for a 50 ft French drain?
About 2.9 cubic yards (4.0 tons) of washed stone for a trench 12 inches wide and 18 inches deep, after allowing for the pipe and 10% extra.
What slope does a French drain need?
At least 1 inch of fall for every 8 feet (about 1%), all the way to an outlet. Without a slope and an outlet the drain fills with water and does nothing.
Do I need filter fabric around a French drain?
Yes, wrap the stone in non-woven geotextile so soil cannot wash in and clog it. This trench takes about 250 ft² of fabric, including the overlap.
Which way do the holes in the pipe face?
Down, in the usual instruction for rigid perforated pipe, so water enters from below and flows along the bottom. Some makers specify otherwise, so check the pipe.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.