Stone calculator
Stone Backfill Calculator
Backfill stone is the clean drainage rock behind a wall or around a pipe. Enter the backfill zone dimensions to get tonnage and delivered cost.
Your project
Wall drainage zones are 12" wide minimum. Pipe bedding runs 4-6" under and over the pipe.
Crews typically order 5-10% extra to cover compaction, spillage and uneven subgrade.
Delivered stone backfill typically runs $28-$60 per ton.
Stone backfill needed
25.2
US tons · includes 5% waste
- Area
- 480 sq ft
- Volume
- 18.67 cubic yards
- Volume (cubic feet)
- 504 cu ft
- Total weight
- 50,400 lb
- Density used
- 100 lb per cu ft (1.35 tons/yd³)
- Truckloads (15-ton)
- 2
- Estimated delivered cost
- $1,109
Quarry densities vary by source and moisture. Confirm tons per cubic yard with your supplier before placing a bulk order — a 10% density difference is a whole extra load on a big job.
The shareable link reopens this calculator with your exact inputs.
What stone backfill is
Backfill stone is clean, angular, open-graded aggregate — usually #57 or 3/4" clean — with the fines washed out so water moves through it freely. That void space is the whole point: it relieves hydrostatic pressure behind a wall instead of letting saturated soil push on it.
At 100 lb per cubic foot, one cubic yard weighs about 1.35 US tons, and one ton spread 2" deep covers roughly 120 square feet.
How to install it
Place a minimum 12 inch wide column of clean stone directly behind the wall face, wrapped in non-woven geotextile so soil fines cannot migrate in and clog it. Run a perforated drain pipe at the base of that column, daylighted to grade.
The mistake that costs the most
Backfilling with the soil that came out of the excavation. Native clay holds water, freezes, expands and is the single most common cause of retaining wall failure — the wall did not fail structurally, it was pushed over by water it could not release.
The math behind the calculator
Square feet × (depth in inches ÷ 12) = cubic feet. Cubic feet ÷ 27 = cubic yards. Cubic feet × 100 ÷ 2,000 = US tons. The waste allowance is applied to the volume before the weight conversion, which is how suppliers quote it.
Stone backfill needed per 100 square feet
At 100 lb per cubic foot, before waste.
| Depth | Cubic feet | Cubic yards | Tons |
|---|---|---|---|
| 1" | 8.3 | 0.31 | 0.42 |
| 2" | 16.7 | 0.62 | 0.83 |
| 3" | 25 | 0.93 | 1.25 |
| 4" | 33.3 | 1.23 | 1.67 |
| 6" | 50 | 1.85 | 2.5 |
| 12" | 100 | 3.7 | 5 |
Recommended depth by application
| Application | Depth |
|---|---|
| Segmental wall drainage zone | 12" wide, full wall height |
| Foundation perimeter drain | 12-18" wide |
| Pipe bedding under pipe | 4-6" |
| Pipe cover over crown | 6-12" |
Frequently asked questions
+How many tons of stone backfill do I need?
Multiply square feet by depth in feet to get cubic feet, then multiply by 100 and divide by 2,000. A 500 sq ft area at 12" needs about 25 tons before waste.
+How many tons of stone backfill are in a cubic yard?
Roughly 1.35 tons at 100 lb per cubic foot. Wet material weighs 5-10% more, which matters when you are buying by the ton and measuring by the yard.
+How deep should stone backfill be?
Segmental wall drainage zone: 12" wide, full wall height. Foundation perimeter drain: 12-18" wide. Pipe bedding under pipe: 4-6". Pipe cover over crown: 6-12".
+What does stone backfill cost?
$28 – $60 per ton delivered in most US markets, before the haul fee. Short loads carry a minimum charge, so half a load often costs nearly as much as a full one.
+How wide should the drainage zone behind a retaining wall be?
Twelve inches of clean stone measured from the back of the block, for the full height of the wall, is the industry minimum. Taller walls and clay soils get 18-24 inches. Always separate stone from soil with non-woven filter fabric.