Find out how much gravel, landscape fabric, and pipe you need for a French drain. Enter your trench size to get cubic yards, tons, and bags.
0cu yd
| Item | Amount |
|---|---|
| Gravel by volume | |
| Gravel by weight | |
| Bagged gravel (0.5 cu ft bags) | |
| Estimated gravel cost | |
| Landscape fabric | |
| Perforated pipe |
A French drain is a trench filled with gravel, usually with a perforated pipe along the bottom. The calculator finds the trench volume, subtracts the pipe, and leaves room on top for soil.
Gravel volume = (width × fill depth − pipe area) × length
Fill depth is the trench depth minus the top cover. The result is increased by your settling allowance, then converted to cubic yards, tons, and bags.
The fabric estimate lines the trench and includes 12 inches of overlap across the top.
A 12 inch wide, 18 inch deep trench with a 4 inch pipe and 3 inches of top cover needs about 2.4 cubic yards (roughly 3.3 tons) for every 50 feet, including a 10 percent settling allowance. Enter your own numbers above for a precise figure.
Installers differ, but many recommend holes facing down so water enters from the bottom and flows along the pipe. Follow the pipe maker's instructions.
Clean, washed, angular stone drains best. Common choices are 3/4 inch or 1 inch drain rock. Avoid pea gravel with sand mixed in, since it can clog.
Most installations use it to keep soil from washing into the gravel and clogging the drain. Wrap the fabric over the top of the gravel before adding soil.
A common guideline is about 1 inch of drop for every 8 feet of length, or roughly 1 percent. Check local guidance for your site.