Stone calculator
French Drain Stone Calculator
Size the trench, get the stone. Enter the trench footprint as your area (length × width) and the stone depth to plan a French drain.
Your project
Typical trench: 12" wide, 18-24" deep, with 2-3" of stone under the pipe.
Crews typically order 5-10% extra to cover compaction, spillage and uneven subgrade.
Delivered french drain stone typically runs $28-$60 per ton.
French drain stone needed
37.8
US tons · includes 5% waste
- Area
- 480 sq ft
- Volume
- 28 cubic yards
- Volume (cubic feet)
- 756 cu ft
- Total weight
- 75,600 lb
- Density used
- 100 lb per cu ft (1.35 tons/yd³)
- Truckloads (15-ton)
- 3
- Estimated delivered cost
- $1,663
Quarry densities vary by source and moisture. Confirm tons per cubic yard with your supplier before placing a bulk order — a 10% density difference is a whole extra load on a big job.
The shareable link reopens this calculator with your exact inputs.
What french drain stone is
A French drain is a gravel-filled trench with a perforated pipe at the bottom that intercepts water and carries it somewhere harmless. The gravel must be clean and open-graded — #57 stone, 3/4" clean or 1" clean. Pea gravel works but shifts; crusher run does not work at all because the fines seal it.
At 100 lb per cubic foot, one cubic yard weighs about 1.35 US tons, and one ton spread 2" deep covers roughly 120 square feet.
How to install it
Dig with consistent fall — 1% minimum, meaning 1 inch of drop every 8 feet. Line the trench with non-woven geotextile, bed 3 inches of stone, lay the perforated pipe holes down, fill with stone to within 2-3 inches of grade, fold the fabric over the top, then cap with soil or decorative stone.
The mistake that costs the most
Skipping the fabric or wrapping only the pipe. A sock on the pipe clogs from the outside within a few seasons; wrapping the whole stone envelope keeps silt out of the voids and is what makes a drain last twenty years instead of three.
The math behind the calculator
Square feet × (depth in inches ÷ 12) = cubic feet. Cubic feet ÷ 27 = cubic yards. Cubic feet × 100 ÷ 2,000 = US tons. The waste allowance is applied to the volume before the weight conversion, which is how suppliers quote it.
French drain stone needed per 100 square feet
At 100 lb per cubic foot, before waste.
| Depth | Cubic feet | Cubic yards | Tons |
|---|---|---|---|
| 1" | 8.3 | 0.31 | 0.42 |
| 2" | 16.7 | 0.62 | 0.83 |
| 3" | 25 | 0.93 | 1.25 |
| 4" | 33.3 | 1.23 | 1.67 |
| 6" | 50 | 1.85 | 2.5 |
| 12" | 100 | 3.7 | 5 |
Recommended depth by application
| Application | Depth |
|---|---|
| Standard yard drain | 12" wide × 18" deep |
| Foundation / footing drain | 12-18" wide × to footing depth |
| Driveway edge interceptor | 8-12" wide × 12-18" deep |
| Stone under the pipe | 2-3" |
Frequently asked questions
+How many tons of french drain stone do I need?
Multiply square feet by depth in feet to get cubic feet, then multiply by 100 and divide by 2,000. A 500 sq ft area at 18" needs about 37.5 tons before waste.
+How many tons of french drain stone are in a cubic yard?
Roughly 1.35 tons at 100 lb per cubic foot. Wet material weighs 5-10% more, which matters when you are buying by the ton and measuring by the yard.
+How deep should french drain stone be?
Standard yard drain: 12" wide × 18" deep. Foundation / footing drain: 12-18" wide × to footing depth. Driveway edge interceptor: 8-12" wide × 12-18" deep. Stone under the pipe: 2-3".
+What does french drain stone cost?
$28 – $60 per ton delivered in most US markets, before the haul fee. Short loads carry a minimum charge, so half a load often costs nearly as much as a full one.
+How much gravel do I need for a 100 ft French drain?
A 100 ft trench 12" wide with 18" of stone holds 150 cubic feet — about 5.6 cubic yards, or roughly 7.5 tons of #57 stone. Add 10% because trench walls are never as neat as the tape measure suggests.
+What size gravel is best for a French drain?
#57 stone (3/4" clean, washed) is the standard. It has around 35-40% void space, is large enough not to enter the pipe perforations and is available at every quarry. Avoid crusher run, screenings or anything described as "minus" — those contain fines that seal the drain.