French Drain Gravel Calculator
Estimate washed drain rock tonnage for yard drainage trenches, foundation curtain drains, and retaining wall backfill.
How much gravel do you need for a French drain?
A 50 ft long × 18 in wide × 18 in deep French drain trench holds about 4.17 cubic yards, which is roughly 5.4 tons of washed 1"–1.5" drain rock at 2,600 lbs/yd³ — before subtracting the ~4% displaced by a 4-inch perforated pipe.
Cubic yards = Length (ft) × Width (ft) × Depth (in) ÷ 12 ÷ 27 · Tons = Cubic yards × 1.3 (washed drain rock)
- Trench volume in cubic feet: 50 × 1.5 × 1.5 = 112.5 cu ft
- Convert to cubic yards: 112.5 ÷ 27 = 4.17 yd³
- Convert to tons: 4.17 × 1.3 (drain rock at 2,600 lbs/yd³) = 5.4 tons
- Add a 10% waste and settling buffer → order about 6 tons
| Trench Width × Depth | Cubic Yards | Tons (approx.) |
|---|---|---|
| 12" × 18" | 5.2 yd³ | 6.8 tons |
| 18" × 24" | 10.8 yd³ | 14.0 tons |
| 24" × 36" | 21.9 yd³ | 28.5 tons |
Table figures subtract the 4-inch perforated pipe (0.087 cu ft per linear ft) and use washed drain rock at 1.3 tons per cubic yard. The calculator below uses gross trench volume without subtracting the pipe; that roughly 4–6% difference is covered by the recommended 10% waste and settling buffer.
1. Select Project Shape
2. Enter Dimensions
3. Select Gravel Aggregate & Density
4. Add Waste & Compaction Buffer
Gravel Layer & Excavation Cross-Section Simulator
Visualize multi-layer ground excavation, plate compaction settling, and dump truck hauling logistics in real-time.
To achieve a final compacted depth of 6.0 inches, you must spread 7.1 inches of loose uncompacted aggregate before running the plate compactor.
Recommended Depth & Base Specifications for French Drain Gravel Calculator
Selecting the proper installation depth is the single most critical factor in preventing premature rutting, sinking, or weed breakthrough.
| Layer / Application | Recommended Depth | Stone Aggregate Type | Contractor Notes |
|---|---|---|---|
| Pipe Bedding Layer | 2 to 3 Inches | 1" Washed Drain Rock | Level bedding laid before setting the 4-inch perforated drain pipe. |
| Pipe Surrounding & Cover | 8 to 14 Inches | 1" - 1.5" Washed Rock | Fills trench sides and covers pipe to intercept groundwater flow. |
| Top Surface Layer | 3 to 4 Inches | Pea Gravel or Topsoil | Wrap the gravel column with non-woven geotextile before topping with soil or decorative stone. |
💡 Contractor Installation Pro Tips
- Always use round or angular washed stone with zero fines (sand/dust); fines will wash into the pipe and cause clogging.
- A 4-inch perforated PVC or corrugated pipe displaces approximately 0.087 cubic feet of volume per linear foot of trench.
- Line the entire trench with non-woven needle-punched geotextile fabric to permanently prevent native soil intrusion into the gravel pore spaces.
Frequently Asked Questions About French Drain Gravel Calculator
What is the best gravel size for a French drain?
The ideal size is 3/4" to 1.5" washed round rock or washed #57 crushed stone. Avoid crusher run or stone with fine dust.
How much gravel for a 100 ft French drain trench?
A 100 ft long x 1 ft wide x 1.5 ft deep trench (approx. 150 cu ft volume minus pipe displacement) requires roughly 5.2 cubic yards or 6.8 tons of washed drain rock.
How do I convert cubic yards of drain rock to tons?
Multiply cubic yards by 1.3 — washed 1"–1.5" drain rock weighs about 2,600 lbs per cubic yard (1.3 tons). For example, the 4.17 cubic yards from a 50 ft × 18 in × 18 in trench equals roughly 5.4 tons.
How wide and deep should a French drain trench be?
Most residential French drains are dug 12 to 24 inches wide and 12 to 36 inches deep, with about a 1% slope (roughly 1 inch of fall per 8–10 feet) so water flows to the outlet. The 4-inch perforated pipe sits on a 2–3 inch bedding layer of wash rock.
How much volume does the perforated pipe take up?
A 4-inch perforated pipe displaces about 0.087 cubic feet per linear foot — roughly 8.7 cubic feet (0.32 cubic yards) per 100 ft, or under 6% of a typical 12 in × 18 in trench. You can ignore it when ordering and let the waste buffer cover it.
Missing a Stone Type or Have Feedback?
We update density presets and formulas regularly based on local quarry feedback.