Multiply trench length × width in feet by backfill depth in feet, divide by 27 for cubic yards, then multiply by 1.45 for tons of #57 stone. A 25 ft trench, 2 ft wide and filled 12 inches deep, takes about 1.85 cubic yards — roughly 2.7 tons.
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Order – tons (includes your waste allowance) so compaction and spillage don’t leave you short.
Stone Backfill Calculator Guide
Backfill is the stone you never see again: it disappears behind retaining walls, around foundation drains, and over utility pipes, where its only job is to carry water away and support the soil above. Because trenches are measured in feet of run rather than square feet of area, this calculator is set up trench-style — length, width, and backfill depth — and converts the result to tons of clean #57 stone by default.
The material choice is the part people get wrong. Backfill that must drain — which is nearly all of it — needs washed, open-graded stone. Its voids are the drainage system. Dense material with fines belongs under structures, not behind or around them.
How Many Tons of Stone Does a Trench Take?
Work per 10-foot run and the numbers stay easy to scale. At 1.45 tons per cubic yard for #57 stone, here is what common trench sections hold:
| Trench section | Per 10 ft of run | Tons of #57 |
|---|---|---|
| 12 in wide × 12 in deep | 0.37 yd³ | 0.5 |
| 18 in wide × 12 in deep | 0.56 yd³ | 0.8 |
| 24 in wide × 12 in deep | 0.74 yd³ | 1.1 |
| 24 in wide × 24 in deep | 1.48 yd³ | 2.1 |
| 36 in wide × 24 in deep | 2.22 yd³ | 3.2 |
Remember to subtract the pipe. A 4-inch drain pipe displaces about 0.9 cubic feet per 10 feet — negligible — but a 12-inch culvert takes out nearly 8 cubic feet per 10-foot run, enough to change the order.
The Right Backfill Sequence for Drains and Walls
- Line the trench with non-woven geotextile, leaving flaps long enough to fold over the top.
- Bed the pipe on 2–3 inches of stone so it holds its slope.
- Surround it with stone to at least 3 inches over the crown, perforations facing down.
- Fold the fabric closed before capping with soil, so the stone zone stays clean for decades.
- Behind retaining walls, carry the stone zone 12 inches back from the wall face for its full height, with a drain pipe at the base.
Clean stone does not compact much, so a 5% allowance covers spillage and over-dig. For the properties of the stone itself, the #57 stone calculator covers the standard drainage grade, and the crushed stone calculator handles the dense material for the base under the wall.
Frequently Asked Questions
Why use washed stone for backfill?
Clean washed stone like #57 keeps 30–40% of its volume as open voids, so water moving toward a pipe or foundation passes straight through instead of building pressure. Stone with fines would compact tight and hold water exactly where you do not want it.
How much stone does 10 feet of trench take?
A trench 2 feet wide filled 12 inches deep holds 20 cubic feet per 10-foot run — about 0.74 cubic yards, or roughly 1.1 tons of #57 stone. Halve the width or depth and the tonnage halves with it.
Do I need filter fabric around stone backfill?
Yes. Wrap the stone zone in non-woven geotextile so surrounding soil cannot wash into the voids. Without it, fines migrate into the stone within a few seasons and the drainage layer slowly seals itself.
Can I backfill a retaining wall with crusher run?
Use crusher run only under the wall as a base. The 12-inch zone directly behind the wall should be clean #57 stone so water drains down to the weep holes or drain pipe instead of pushing against the structure.