Gravel for 50 ft drain at 12×18 in?
About 75 cu ft (2.78 cu yd).
French drain gravel fill is **trench length × width × depth**. Measure run length in feet, trench width in feet (12 in = 1 ft), and gravel fill depth in inches.
**Imperial formula:**
Cubic feet = Length (ft) × Width (ft) × Depth (in) ÷ **12**
Cubic yards = cu ft ÷ **27**
**Example — 50 ft run, 12 in wide, 18 in deep:**
50 × 1 × 18 ÷ 12 = **75 cu ft** (~2.78 cu yd)
**Typical trench profile:**
Perforated pipe, filter fabric, and outlet fittings are **ordered separately** — this tool estimates drain rock volume only.
Concise answers for common searches — definitions, steps, and comparisons.
About 75 cu ft (2.78 cu yd).
18 inches of drain rock fill in a 12 in wide trench.
The calculator treats the trenched zone as a rectangular prism: run length × trench width × gravel fill depth. An optional buffer covers over-dig and spillage.
Formula
cu ft = L(ft) × W(ft) × D(in) ÷ 12 | cu yd = cu ft ÷ 27Tap Standard trench (12×18 in), Deep trench (12×24 in), or Long foundation run — each sets width and depth.
Measure along the trench centerline from start to outlet — foundation swales, downspout extensions, or yard drains.
Enter width in feet (12 in = 1 ft). Fill depth is gravel depth in the trench, typically 12–24 in.
Bulk suppliers quote drain rock by the cubic yard. Enter bag size for retail pickup counts.
Enable buffer for over-dig and spillage. Order perforated pipe, fittings, and filter fabric separately.
Input
50 ft × 1 ft × 18 inOutput
75 cu ft · 2.78 cu yd50 × 1 × 18 ÷ 12 = 75 cu ft.
Input
100 ft × 1 ft × 18 inOutput
150 cu ft · 5.56 cu ydLong perimeter drain — bulk delivery.
Input
30 ft × 1 ft × 12 inOutput
30 cu ft · 1.11 cu ydShallow extension from downspout.
Input
15 m × 0.3 m × 0.3 mOutput
1.35 m³15 × 0.09 = 1.35 cubic meters.
Common real-world scenarios where this tool saves time.
100 ft along house at 12×18 in: 100 × 1 × 1.5 = 150 cu ft → ~5.6 cu yd. Slope 1% away from foundation to daylight.
30 ft run from downspout at 12×12 in shallow trench: ~30 cu ft (~1.1 cu yd). Daylight or dry well at end.
50 ft standard trench: 75 cu ft (~2.78 cu yd) — default golden vector. Use clean ¾–1½ in drain rock.
15 m × 30 cm wide × 30 cm deep: volume in m³ for EU bulk bag orders.
Step-by-step chains that connect related tools for common tasks.
Trench rock, pipe, and outlet.
| Profile | Width | Fill depth | Use |
|---|---|---|---|
| Standard | 12 in | 18 in | Yard and foundation drains |
| Shallow | 12 in | 12 in | Downspout extensions |
| Deep | 12 in | 24 in | High water table areas |
| Narrow | 6 in | 18 in | Tight side-yard runs |
Wider trenches improve flow capacity — confirm with local code.
Every drain needs a positive outlet — never dead-end a French drain without an engineered dry well.
Lay perforated pipe with holes at 4 and 8 o'clock so water enters from the trench bottom.
Place rock around pipe, cover 2 in above pipe, then fold fabric and backfill soil.
Use **clean angular drain rock** (¾–1½ in) — fines clog perforated pipe and reduce flow.
Maintain **minimum 1% slope** (1 in per 8 ft) to outlet, dry well, or daylight.
Wrap pipe and trench with geotextile to prevent soil infiltration into the rock bed.
Call **811** before digging — deep foundation trenches cross gas, electric, and water lines.
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At 12 in wide × 18 in deep: about 75 cu ft or 2.78 cubic yards. Add 10% buffer for over-dig.
12 inches is standard for residential yard drains. Narrow 6 in trenches work for tight runs but reduce flow capacity.
18 inches gravel fill is typical — deep enough to capture subsurface water and bury perforated pipe. Shallow 12 in works for downspout extensions.
Clean angular drain rock, ¾–1½ inch. Avoid pea gravel, limestone screenings, and crusher fines that clog pipe.
No. This calculator estimates drain rock volume only. Order 4 in perforated pipe, fittings, and filter fabric separately.
Minimum 1% (1 in drop per 8 ft run) toward daylight, storm drain, or an engineered dry well.
Trench dimensions are processed only in your browser — EverydayTools does not collect or store your measurements.
Volume estimates only — not civil engineering or drainage design. Confirm outlet design and local codes with a qualified contractor.
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Reviewed on 2026-06-28.
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Trench profile
12 in wide × 18 in deep — typical yard drain.
Gravel fill depth presets
Depth of drain rock in the trench — typically 12–24 in including pipe zone.
Bagged drain rock — often 0.5 cu ft. Leave blank to skip bags.
1 cubic yard covers
| Depth | Sq ft |
|---|---|
| 1 in | 324 |
| 2 in | 162 |
| 3 in | 108 |
| 4 in | 81 |
Bag coverage at 18 in depth
| Bag | Covers | Per cu yd |
|---|---|---|
| 1 cu ft bag | 1 sq ft | 27 bags |
| 1.5 cu ft (40 L) | 1 sq ft | 18 bags |
| 2 cu ft bag | 1 sq ft | 14 bags |
| 3 cu ft bag | 2 sq ft | 9 bags |