Gravel quantity depends on trench dimensions. A standard trench is 12 inches wide × 24 inches deep. For every 10 linear feet at those dimensions: volume = 1 ft × 2 ft × 10 ft = 20 cubic feet = 0.74 cubic yards. Most suppliers sell gravel by the ton (1 cubic yard of crushed stone weighs approximately 1.4 tons). Always add 10% extra for settling and waste.

Most residential French drains use 4-inch perforated pipe (corrugated or PVC). For large areas or high water volume, use 6-inch pipe. Corrugated flexible pipe is easier to install on curves, while rigid PVC is more durable long-term and resists crushing. Both work well when properly installed.

French drain depth depends on the problem being solved. For surface water and yard drainage: 18–24 inches is usually sufficient. For protecting foundation walls from hydrostatic pressure: the drain should be at or below the footing level, typically 4–6 feet deep. The deeper the drain, the more gravel and labor required.

Not always. A simple French drain can be just a gravel-filled trench without pipe — called a "French drain" or "curtain drain." However, adding perforated pipe significantly improves drainage capacity and longevity. For most residential applications, use perforated pipe for best results, especially if handling significant water volume.