How to calculate a retaining wall backfill
Clean crushed stone behind a retaining wall lets water drain through instead of pushing the wall over.
- Measure the wall length and the height of the stone zone behind it.
- Enter the width of the stone zone, commonly 12 inches.
- Add the base leveling pad as a second calculation.
- Order washed, angular stone.
Worked example
For a typical retaining wall backfill with length 30 ft, width 12 in, depth 36 in, the volume is 90.00 cubic feet. Divide by 27 for 3.33 cubic yards. With a 10 percent allowance, plan for 3.67 cubic yards.
In crushed stone, 3.33 cubic yards weighs about 4.50 US tons at a planning value of 2,700 pounds per cubic yard.
Retaining Wall Backfill sizes and quantities
These common sizes are calculated with the same formula as the tool above, so you can find your number quickly.
| Size | Cubic feet | Cubic yards | With 10 percent extra | US tons |
|---|---|---|---|---|
| 20 ft, 12 in wide, 24 in high | 40.00 | 1.48 | 1.63 | 2.00 |
| 30 ft, 12 in wide, 36 in high | 90.00 | 3.33 | 3.67 | 4.50 |
| 50 ft, 12 in wide, 48 in high | 200.00 | 7.41 | 8.15 | 10.00 |
| 80 ft, 18 in wide, 48 in high | 480.00 | 17.78 | 19.56 | 24.00 |
Tips
- Follow the wall manufacturer or engineer for width and stone size.
- Tall walls over about 4 feet often need an engineer.
- Compact in lifts as you build up the wall.
Common mistakes to avoid
- Backfilling with the soil you dug out.
- Skipping the drain pipe at the base.
- Forgetting the leveling base under the first course.
These figures are planning estimates. Real material varies in moisture, size, and compaction, so confirm weights and order quantities with your supplier.
Frequently asked questions
How many cubic yards do I need for a retaining wall backfill?
Multiply the dimensions in feet and divide by 27. The example above, length 30 ft, width 12 in, depth 36 in, needs 3.33 cubic yards before waste.
How much extra should I order?
Add 5 to 10 percent for waste. Add more if the ground is uneven or the material is loose.
Can I enter inches and feet together?
Yes. Each box has its own unit selector, so you can mix feet and inches.
How much does retaining wall backfill material weigh?
3.33 cubic yards of crushed stone weighs about 4.50 US tons as a planning value.