Free Calculator
Retaining Wall Backfill Calculator — How Much Stone Behind the Wall?
Tons of clean #57 stone for the drainage column behind your wall.
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 retaining wall needs a 12-inch column of clean angular stone immediately behind it for drainage and to keep hydrostatic pressure off the wall. Use this calculator to size the stone for that column.
How to use this retaining wall backfill calculator
- 1
Measure the wall length
Total run of the wall in feet.
- 2
Set the column width
Default is 12 inches (1 foot). Use width = 1 foot in the calculator. Stiffer walls or wetter soils may use 18 inches.
- 3
Set the wall height
Use wall height as the depth. A 3-foot wall = 36-inch depth. A 4-foot wall = 48-inch depth.
- 4
Pick the stone
#57 is standard. #4 is better in heavy clay or wet sites where flow rate matters.
- 5
Enter your ZIP
Florida ZIPs return delivered pricing.
How the math works
Stone volume in cubic yards equals Wall Length × Column Width × Wall Height ÷ 27, with all dimensions in feet.
A 30 ft long × 4 ft tall wall with a 12" column = 30 × 1 × 4 = 120 cu ft = 4.4 cu yds ≈ 6 tons of #57 stone.
Wrap the stone column in non-woven geotextile fabric. Add a perforated drain pipe at the base with a daylight outlet — the column without an outlet just collects water against the wall.
How much does retaining wall backfill 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 |
|---|---|---|---|
| 20 ft long × 3 ft tall wall | 36" | 20 sq ft | ~3 tons #57 |
| 30 ft long × 4 ft tall wall | 48" | 30 sq ft | ~6 tons #57 |
| 50 ft long × 4 ft tall wall | 48" | 50 sq ft | ~10 tons #57 |
| 40 ft long × 6 ft tall wall | 72" | 40 sq ft | ~12 tons #57 |
| 100 ft long × 3 ft tall wall | 36" | 100 sq ft | ~13 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 drainage column at all
Soil packed directly against a retaining wall traps water and pushes the wall over within a few seasons. The stone column is not optional.
No fabric
Soil fines migrate into bare stone and clog the drainage. Wrap the stone with geotextile fabric.
No drain pipe
A stone column without an outlet pipe is a French drain with no drain. Add a 4-inch perforated pipe at the base, sloped to a daylight outlet.
Wrong stone
Crusher run or any stone with fines defeats the purpose. Use washed #57 or #4.
Stopping the column too low
The stone column should rise to within one course of grade and then be capped with topsoil. Stopping low traps surface water in the column.
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.