French Drain Gravel Calculator
A French drain gravel calculator multiplies trench length × width × depth ÷ 27, then × 1.4 for tons: a 30 ft trench 1 ft wide and 12 in deep needs 1.56 tons.
What your order looks like
A pickup or a small delivery will do it.
1.11 yd³ · 1.6 tons
15 wheelbarrow trips (2 cu ft each)
3 pickup loads (0.75 ton each)
1 small dump truck load (6 tons each)
Rules of thumb: A wheelbarrow trip is 2 cubic feet of heavy material, about 200 lb, a load most people can push. A pickup load is 0.75 ton, the payload of a full-size half-ton pickup (1,500 lb). A small single-axle dump truck carries about 6 tons.
How much gravel do I need for a French drain?
This French drain gravel calculator fills the trench by volume, then converts to weight: cubic yards = length × width × (depth in inches ÷ 12) ÷ 27, and tons = cubic yards × 1.4. A 30 ft trench that is 1 ft wide and 12 inches deep needs 1.11 cubic yards, or 1.56 tons of gravel. With the 10% waste box ticked it is 1.71 tons, costing $77.00 at $45 per ton.
Enter the trench length and width in feet, the dug depth in inches, and your price per ton.
The formula in plain words
A French drain trench is a long, narrow box filled with stone. The calculator:
- Turns depth into feet: inches ÷ 12.
- Multiplies length × width × depth for cubic feet.
- Divides by 27 for cubic yards.
- Multiplies by 1.4 tons per cubic yard, a typical weight for washed gravel.
- Adds 10% if the waste box is ticked, then prices it.
If you use #57 stone, which this site figures at 1.35 tons per yard, your order will be slightly lighter: about 3.5% fewer tons for the same trench.
Worked examples
- Default: 30 ft × 1 ft × 12 in, $45/ton
- Cubic feet: 30 × 1 × 1 = 30 ft³
- Cubic yards: 30 ÷ 27 = 1.11 yd³
- Tons: 1.11 × 1.4 = 1.56 tons, costing $70.00
- With 10% waste: 1.71 tons, costing $77.00
- Yard drain: 80 ft × 1.5 ft × 18 in, $45/ton
- Depth: 18 ÷ 12 = 1.5 ft
- Cubic feet: 80 × 1.5 × 1.5 = 180 ft³
- Cubic yards: 180 ÷ 27 = 6.67 yd³
- Tons: 6.67 × 1.4 = 9.33 tons, costing $420.00
- With 10% waste: 10.27 tons, costing $462.00
Gravel per 10 ft of trench
| Trench width × depth | Cubic yards per 10 ft | Tons per 10 ft (1.4 t/yd³) |
|---|---|---|
| 12 × 12 in | 0.37 | 0.52 |
| 12 × 18 in | 0.56 | 0.78 |
| 12 × 24 in | 0.74 | 1.04 |
| 18 × 18 in | 0.83 | 1.17 |
| 18 × 24 in | 1.11 | 1.56 |
Multiply by your trench length ÷ 10. Figures are net, before waste.
What goes in the trench
| Layer, bottom to top | Typical amount |
|---|---|
| Filter fabric lining the trench | Enough to wrap over the top |
| Bedding stone | About 2 inches |
| Perforated pipe, holes usually facing down | 4 inch is common for homes |
| Stone around and over the pipe | To within a few inches of grade |
| Fabric folded over | Overlapped on top |
| Topsoil and sod, or more stone | Finish layer |
If you finish with soil and sod, subtract that top layer from the depth you enter, since it is not gravel.
How to measure your trench
- Length: walk the route with a measuring wheel from the high end to the outlet.
- Width: a trenching shovel or rented trencher sets it. Measure across the top.
- Depth: measure from grade to the trench floor at both ends and in the middle. The trench gets deeper as it slopes, so use the average.
- Fall: check it with a string line and line level, or the drainage slope calculator.
Common mistakes
- Using stone with fines. It packs solid and stops draining.
- No fall, or a dip. A low spot in the middle holds water.
- No outlet. The drain must empty somewhere lower: daylight, a dry well, or an approved storm connection. Check local code before tying into storm drains.
- Ordering by volume but paying by weight. Quarries usually sell by the ton, so order the tons figure.
Related calculators
For the whole job, the French drain cost calculator adds pipe and labor. Pricing other drainage stone? See the #57 stone calculator or drain rock calculator. For the fabric, use the landscape fabric calculator.
Frequently asked questions
What should I enter for Length and Width on a trench?
Length is the trench's total run in feet, from the high end to the outlet. Width is the dug width in feet: 12 inches is 1 ft and 18 inches is 1.5 ft. Depth is the full dug depth in inches. A 30 ft trench, 1 ft wide and 12 inches deep, needs 1.56 tons of gravel.
What kind of gravel should I use in a French drain?
Clean, washed stone with no fines, such as #57 stone or washed drain rock around ¾ to 1½ inches. Avoid crusher run, road base, and anything sold as compactable, because the fines clog the gaps and the pipe.
How wide and deep should a French drain trench be?
Many residential drains are dug about 12 inches wide and 12 to 18 inches deep, with the pipe near the bottom on a couple of inches of stone and stone filled over the top. Deeper or wider trenches are used where more water must move or the outlet is far away.
Do I need to subtract the pipe's volume?
Usually not. A 4-inch pipe takes up about 0.087 square feet of cross-section, roughly 9% of a 12 × 12 inch trench. Over 30 ft that is about 2.6 cubic feet, or 0.14 tons of gravel, which the 10% waste allowance covers.
Does the trench need a slope for the water to drain?
Yes. Water moves by gravity, so the trench bottom must fall steadily toward the outlet. A common minimum is about 1%, which is 1 ft of drop per 100 ft, or about 1/8 inch per foot. A 30 ft drain falls about 3.6 inches.
Should I wrap the gravel and pipe in landscape fabric?
In most soils, yes. Line the trench with non-woven filter fabric, add the stone and pipe, then fold the fabric over the top. It keeps silt from washing into the stone. Check that the fabric is rated for drainage, not just weed control.
Estimates only. Verify quantities with your supplier before purchasing.