Drainage Gravel Calculator
Plan your drainage project with accurate material estimates. Enter your trench dimensions to get gravel tonnage, pipe length, landscape fabric, and total material cost for French drains, curtain drains, and dry wells.
French Drain vs Curtain Drain
A French drain collects and redirects groundwater that is already in the soil, typically used near foundations and in waterlogged areas. A curtain drain intercepts surface water flowing downhill before it reaches a structure, installed at a right angle to the water flow path. Both use the same construction method: a gravel-filled trench with a perforated pipe wrapped in geotextile fabric. The main difference is placement and purpose. In many yard drainage situations, a curtain drain installed upslope is more effective than a French drain next to the house.
Dry Well Design Basics
A dry well is a large underground chamber filled with gravel that collects stormwater and allows it to percolate into the soil. Size the well to hold the runoff volume from your roof or paved area. A typical residential dry well is 3 feet in diameter and 3 feet deep, holding about 21 cubic feet of gravel. Factor in 40 percent void space in the gravel, giving you roughly 8 cubic feet of water storage capacity. Multiple smaller dry wells connected by pipe often work better than one large one. Place dry wells at least 10 feet from foundations.
Frequently Asked Questions
What size gravel for a French drain?
Use 3/4-inch to 1-1/2-inch washed stone (no fines). Pea gravel also works but provides less void space. Never use crusher run, as the fines clog over time.
How deep should a French drain be?
Residential French drains are typically 18 to 24 inches deep. For foundation drainage, dig to the bottom of the footing. Maintain a minimum 1 percent slope (1 inch per 8 feet) toward the outlet.
Do I need landscape fabric around the gravel?
Yes. Wrap the trench with non-woven geotextile fabric to prevent soil from migrating into the gravel and clogging the system. This is the most important step for long-term performance.