Gravel for a French Drain
Free calculator with pre-filled dimensions • Updated March 2026
A 30-foot French drain (12" wide, 18" deep) needs about 1.67 cubic yards (2.3 tons) of drainage gravel.
Open calculator with these dimensions →French Drain Gravel Guide
A French drain is a gravel-filled trench with a perforated pipe that redirects groundwater away from foundations, yards, and low areas. A 30-foot drain at 12 inches wide and 18 inches deep requires 1.67 cubic yards of clean drainage stone.
Correct Stone for French Drains
Use #57 washed stone (3/4" to 1"). This size allows rapid water flow while supporting the pipe. Never use crusher run or pea gravel — fines clog the pipe perforations within 1–2 years.
Material List
| Material | Quantity | Cost (2026) |
|---|---|---|
| #57 washed stone | 2.3 tons | $55–$88 |
| 4" perforated drain pipe | 30 feet | $15–$30 |
| Filter fabric sock | 30 feet (or wrap fabric) | $12–$25 |
| Landscape fabric | 1 roll | $15–$25 |
Total: $100–$170 for materials. Professional installation: $25–$50 per linear foot ($750–$1,500 for 30 feet).
Installation
- Plan slope: 1% minimum grade (1 inch drop per 8 feet). The drain must slope toward a discharge point — dry well, storm drain, or daylight outlet.
- Dig trench: 12" wide × 18" deep. Wider is better for severe drainage issues.
- Line with fabric: Lay landscape fabric in the trench with excess on both sides to fold over the top.
- Add base gravel: 3" of #57 stone on the bottom. Place perforated pipe (holes down). Fill remaining space with stone. Fold fabric over the top.
Pro Tips
- Holes down, not up. The perforated pipe collects water that rises from below, not water that falls from above. Orient perforations at 4 and 8 o'clock positions.
- Use a filter fabric sock on the pipe if you don't wrap the entire trench in fabric. This prevents silt from entering and clogging the pipe over the 20+ year life of the drain.
- Never connect to the sewer system. French drains must discharge to daylight, a dry well, or a storm drain — not the sanitary sewer. Connecting to the sewer is illegal in most areas and can cause backups.
Frequently Asked Questions
What size gravel for a French drain?
#57 washed stone (3/4 to 1 inch) is the standard for French drains. It provides excellent drainage while supporting the pipe. Never use fine gravel, crusher run, or pea gravel — these clog the perforations.
How deep should a French drain be?
Standard depth is 18–24 inches. The drain should be deep enough that the bottom of the trench is below the problem water level. For foundation drainage, the bottom should be at or below the footing level.