Calculate how much gravel, perforated pipe, and landscape fabric you need for a french drain installation. Get results in cubic yards, tons, pipe sections, and estimated material cost. Supports common trench sizes from 6 to 18 inches wide and 12 to 24 inches deep.
Installing a 50-foot french drain with a 12-inch wide, 18-inch deep trench and 4-inch perforated pipe? You need about 2.6 cubic yards (3.7 tons) of #57 stone, 5 sections of drain pipe, and 50 linear feet of landscape fabric. At typical prices, materials run $200–$400.
Based on 12" wide, 18" deep trench with 4" perforated pipe.
| Trench Length | Gravel (yd³) | Gravel (tons) | Pipe (sections) |
|---|---|---|---|
| 25 ft | 1.3 | 1.8 | 3 |
| 50 ft | 2.6 | 3.7 | 5 |
| 75 ft | 3.9 | 5.5 | 8 |
| 100 ft | 5.2 | 7.3 | 10 |
| Material | Typical Price |
|---|---|
| #57 crushed stone (per ton) | $35 – $55 |
| 4" perforated pipe (per ft) | $0.50 – $1.50 |
| Non-woven geotextile fabric (per sq ft) | $0.15 – $0.50 |
| Pipe fittings (couplings, end caps) | $2 – $8 each |
| Pop-up emitter / outlet | $8 – $15 each |
| Catch basin (12×12) | $25 – $50 each |
Most residential french drains are 18 to 24 inches deep. The minimum effective depth is 12 inches, but 18 inches is the standard for yard drainage. If you're protecting a foundation, dig below the footing level — typically 24 inches or more. Deeper drains intercept more groundwater but cost more to install.
#57 crushed stone (3/4-inch washed stone) is the industry standard for french drains. It provides excellent drainage, doesn't compact easily, and won't clog the perforated pipe. Avoid using pea gravel alone — it migrates and can clog over time. River rock works for the top decorative layer but is too large for pipe bedding.
A french drain needs a minimum slope of 1% — that's 1 inch of drop per 8 feet of run, or about 1/8 inch per foot. A slope of 1–2% is ideal. Without adequate slope, water pools in the pipe and the drain won't function. Use a laser level or string line to maintain consistent grade during installation.
Yes, landscape fabric is strongly recommended. It wraps around the gravel to prevent soil and sediment from migrating into the stone and clogging the system. Without fabric, fine soil particles gradually fill the voids between stones and reduce drainage capacity. Use non-woven geotextile fabric — not the cheap woven weed barrier from hardware stores.
A properly installed french drain with landscape fabric and clean washed stone lasts 20 to 40 years. Drains without fabric or with dirty (unwashed) stone may clog in 5 to 10 years. The most common failure is silt infiltration — that's why fabric and washed #57 stone are critical.
Yes — french drains are one of the more DIY-friendly drainage projects. The main challenge is digging the trench, which is labor-intensive. For trenches over 50 feet, consider renting a trenching machine. The key steps are: dig the trench with proper slope, line with fabric, add 2–3 inches of stone, lay the perforated pipe (holes down), fill with stone, and wrap the fabric over the top.
Need a general gravel calculator? See our gravel calculator for driveways, pathways, and landscaping.