[stonecalc id=”stone-backfill”]
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.
[stonecalc_faq id=”stone-backfill”]