[stonecalc id=”retaining-wall”]
Retaining Wall Calculator Guide
A retaining wall is really two stone orders wearing one name. The first is the wall itself — the visible face you enter here as length × height × thickness, returned in cubic yards and tons at a 15% waste allowance. The second is invisible once the job is done: a 12-inch-wide column of washed drainage stone running up the back of the wall, and it is the order most first-time builders forget entirely.
That hidden column is not optional decoration. Retaining walls rarely fail because the stone was too weak; they fail because saturated soil behind them turned into hydraulic pressure with nowhere to go. The drainage stone and the pipe at its base are the pressure-relief valve, which is why an honest estimate prices both orders from the start.
How Much Stone Does a Retaining Wall Need?
| Wall height | Wall stone per 10 ft (24 in thick) | Drainage stone per 10 ft (12 in column) |
|---|---|---|
| 2 ft | ≈ 1.5 yd³ / 2.4 tons | ≈ 0.75 yd³ / 1.1 tons |
| 3 ft | ≈ 2.2 yd³ / 3.6 tons | ≈ 1.1 yd³ / 1.6 tons |
| 4 ft | ≈ 3.0 yd³ / 4.7 tons | ≈ 1.5 yd³ / 2.1 tons |
Wall stone figures use gabion-grade rock at 1.6 tons per cubic yard; the drainage column uses washed #57 at 1.45. To price the drainage order, run the calculator a second time with the wall height unchanged, thickness set to 12 inches, and #57 selected. Four feet is also the ceiling: any wall taller than that — or any wall with a driveway, slope, or building leaning on it from above — belongs to an engineer, not a calculator.
Batter, Base, and Weep Drainage
- Dig the base trench first. Excavate below topsoil and compact 6 inches of crusher run as a footing pad, then bury the entire first course of stone — roughly 10% of the wall height below grade anchors the wall against kick-out.
- Build with batter. Step each course back about 1 inch per foot of height so the wall leans into the slope it restrains. A plumb retaining wall is a wall waiting for its first wet spring.
- Lay the weep system early. Perforated pipe goes at the bottom of the drainage column, holes down, sloped to daylight past the wall ends before any backfill rises above it.
- Fabric between soil and stone. Filter fabric on the soil side keeps fines from silting the drainage column shut over the years — clogged stone behaves like no stone at all.
- Backfill in lifts. Alternate drainage stone against the wall and native soil behind the fabric, compacting lightly every 8 inches rather than dumping the whole depth at once.
Size the compacted footing pad separately with the crusher run calculator, and use the #57 stone calculator if you prefer to price the drainage column as its own line item. Ordering all three materials in one delivery usually beats three small-load fees — and guarantees the drainage stone actually shows up on build day.
[stonecalc_faq id=”retaining-wall”]