Free Calculator
French Drain Calculator — How Much Stone Do I Need?
Tons of #57 or #4 stone for your French drain trench.
3. Enter Dimensions
Your order summary lands here
As soon as the dimensions are valid, you will see the recommended quantity, truckload count, and the ZIP pricing step.
A French drain is a fabric-wrapped trench filled with clean angular stone around a perforated pipe. Use this calculator to size the stone for the trench fill.
How to use this french drain calculator
- 1
Measure the trench
Length of the drain in feet × trench width (usually 12 inches). Use the rectangle option with width = trench width.
- 2
Pick a depth
Trench depth is typically 18–24 inches. Set the depth equal to the trench depth in inches.
- 3
Pick the stone
#57 is standard. Use #4 if maximum flow rate matters and the trench is wide enough for the larger stones.
- 4
Enter your ZIP
Florida ZIPs return delivered pricing per ton.
How the math works
Stone volume in cubic yards equals Trench Length × Trench Width × Trench Depth ÷ 27, with all dimensions in feet.
For a typical 50 ft × 12" wide × 18" deep trench: 50 × 1 × 1.5 = 75 cu ft = 2.8 cu yds ≈ 3.5 tons of #57.
Wrap the trench in geotextile fabric before adding stone. The fabric keeps soil fines out of the stone — without it the drain clogs within a few years.
How much does french drain cover?
Quick reference for how much area one ton and one cubic yard cover at common depths.
| Depth | 1 ton covers | 1 cubic yard covers |
|---|---|---|
| 1" | 231 sq ft | 324 sq ft |
| 2" | 116 sq ft | 162 sq ft |
| 3" | 77 sq ft | 108 sq ft |
| 4" | 58 sq ft | 81 sq ft |
| 6" | 39 sq ft | 54 sq ft |
| 12" | 19 sq ft | 27 sq ft |
Assumes a density of about 1.4 tons per cubic yard, typical for #57 limerock and most washed gravels. Denser crushed stone covers slightly less per ton.
Typical quantities by project
| Project | Depth | Area | Estimate |
|---|---|---|---|
| Backyard drain 50 ft × 12" × 18" | 18" | 50 sq ft | ~3.5 tons #57 |
| Long drain 100 ft × 12" × 24" | 24" | 100 sq ft | ~9 tons #57 |
| Foundation drain 80 ft × 18" × 24" | 24" | 120 sq ft | ~11 tons #57 |
| Driveway edge 60 ft × 12" × 12" | 12" | 60 sq ft | ~3 tons #57 |
| Hillside intercept 40 ft × 12" × 24" | 24" | 40 sq ft | ~4 tons #57 |
Common ordering mistakes
From real deliveries, these are the mistakes we see most often. Avoiding any one of them saves a callback order.
No fabric
Soil fines migrate into bare stone within 2–3 years and choke flow. Geotextile fabric (non-woven, 4 oz/sq yd or heavier) is mandatory.
Wrong stone size
Crusher run or stone with fines defeats the purpose. Use washed #57 or #4 — clean and angular for maximum void space.
Pipe holes facing up
Perforated pipe goes holes down. Water enters through the bottom and is carried away inside the pipe.
No slope
A flat French drain holds water instead of moving it. Slope at least 1% (1 inch drop per 8 feet) from inlet to outlet.
Trench too shallow
A 6-inch trench is decorative, not functional. 18 inches minimum, 24 inches better in clay or heavy-rain Florida soils.
Frequently asked questions
Ready to see delivered pricing?
Jump back to the calculator to price the exact quantity for your ZIP, or request a manual quote if the project needs special handling.