How many tons of stone do I need for a retaining wall?
For a retaining wall 30 ft long and 3 ft high, plan on about 5 US tons of cut or fieldstone, 10 US tons for a solid dry-stack gravity wall, or 13 US tons of 18–24 in boulders. Each example includes a 10% allowance and uses the starting rates in the calculator.
Thin wall stone is estimated from the face area. Boulders are estimated by the number of rows needed to reach the total height. A solid gravity wall fills its full width, so its stone quantity is based on volume.
Wall stone coverage per ton
County Materials lists 20 ft² per US ton for its 8 in natural dry cut wall stone, equivalent to about 2.05 m² per tonne. Landscape Supply lists 20 to 25 ft² per ton for basalt wallstone with a 5 to 12 in bed depth. Use your supplier’s face coverage for the stone and bed depth you plan to order.
A 30 ft × 3 ft wall has 90 ft² of face area. At 20 ft² per US ton, divide 90 by 20 to get 4.50 US tons. Adding 10% gives 4.95 US tons to order.
How many boulders per linear foot?
For a single row, Aquascape’s coverage is about 2 to 25 linear ft per US ton, depending on boulder size.
Aquascape gives coverage per ton without a wall height, so this calculator treats each rate as one row of boulders and multiplies by the number of rows. Check with your stone yard.
| Boulder size (US) | Coverage (ft / US ton) | Boulder size (metric) | Coverage (m / tonne) |
|---|---|---|---|
| 6–12 in | 25 | 15–30 cm | 8.4 |
| 12–18 in | 10 | 30–45 cm | 3.4 |
| 18–24 in | 5 | 45–60 cm | 1.7 |
| 24–36 in | 2 | 60–90 cm | 0.7 |
For a 30 ft × 3 ft wall with 18–24 in boulders, divide the 36 in height by the 21 in midpoint and round up to 2 rows. At 5 ft per US ton, a 30 ft row needs 6 US tons. The two rows need 12.0 US tons, or 13.2 US tons with 10% allowance.
How thick should a dry stone retaining wall be?
Hunker’s estimating rule uses a wall width of two-thirds of its height, so a 3 ft wall starts at about 2 ft wide. Enter the actual width from your project plans when you have it. Wall stability and the required width depend on site conditions and the design.
At 30 ft × 3 ft × 2 ft, the wall volume is 180 ft³, or 6.67 yd³. At 1.4 US tons per yd³, the midpoint of Hello Gravel’s 1.3 to 1.5 tons per yd³ river-rock range, that is 9.33 US tons or 10.27 US tons with 10% allowance. Hunker uses 15 ft³ per ton, equivalent to about 1.8 US tons per yd³. Ask your stone yard for the bulk density of the stone you intend to use.
Base gravel for a stone or boulder wall
Estimate base gravel and behind-wall drainage stone separately from the wall stone. Use the gravel and drainage calculator with the dimensions specified for your project, and check the retaining wall base depth guide to identify which parts of the base and trench to measure.
When a stone wall needs an engineer
Consult a qualified local engineer when local rules require a design or when nearby loads, slopes, weak soils or drainage conditions make wall stability uncertain. Check the retaining wall permit height limits guide for local examples and read the engineering disclaimer for the scope of the material estimate.
Frequently asked questions
How many square feet does a ton of wall stone cover?
County Materials lists 20 ft² per US ton for its 8 in natural dry cut wall stone. Landscape Supply lists 20 to 25 ft² per ton for basalt wallstone with a 5 to 12 in bed depth. Ask your supplier for the face coverage of the product you plan to install.
How many tons of boulders do I need for a 3 foot wall?
A 30 ft long, 3 ft high wall with 18–24 in boulders needs about 12.0 US tons before allowance or 13.2 US tons with 10% added. The estimate uses 2 rows and about 5 linear ft per US ton per row. Change the length and size band to match your wall.
Is a boulder wall cheaper than a block wall?
It depends on local stone and delivery prices. Compare quotes for the same wall length and height, with delivery, unloading, equipment, labor, base and drainage itemized. Ask how the supplier prices the stone and any extra handling. The retaining wall cost per square foot guide explains how to compare estimates on the same basis.
Can I mix boulder sizes?
Yes. Calculate each size band separately for the portion of the wall it will occupy, then add the tonnages. If the sizes are stacked in separate rows, use the height assigned to each band in the layout. For blended rows, ask the stone yard how to split the order by size.
References and scope
Arithmetic and worked examples are explained on our methodology page. The cited sources provide product, pricing or local approval context; they do not approve a generic wall. References checked November 4, 2026.
- County Materials: Natural Dry Cut Wall StoneCoverage for the 8 in dry cut wall stone.
- Landscape Supply: Basalt Regular Wallstone data sheet (PDF)Coverage and bed depth for the basalt wallstone product.
- Aquascape: Quantity of Boulders Used for a Retaining WallApproximate linear coverage by size in US and metric units.
- Hunker: How to Estimate Stone WallsThe two-thirds width assumption and a volume-to-weight example.
- Hello Gravel: River Rock Retaining Wall CalculatorA supplier example range for river rock bulk density.
Read the estimating and engineering limits, or send a correction.