Trench Volume Calculator
Take off a utility trench in one pass: spoil in bank yards (what you dig) and loose yards (what you haul after swell), the bedding material for the depth you specify, and the backfill zone — trench volume minus bedding minus the volume the pipe itself displaces. Volumes are neat-line rectangular geometry; the safety over-dig that OSHA sloping or benching adds is a separate, larger number, and this page says so up front. Free, no login.
Trench
Volumes
Backfill = trench − bedding − pipe displacement. Loose spoil adds 25% swell (typical planning figure — swell 25% (typ 15–30%), shrink 10% (typ 5–15%)).
Volumes are neat-line trench geometry only — they exclude OSHA sloping/benching over-dig and shoring. OSHA 1926 Subpart P governs. See the excavation reference charts.
Trench — Haul Sheet
Prepared with NORDIX — nordixhq.com/tools/trench-calculator
Trench: 24" W × 48" D × 100 ft · Bedding: 6 in · Pipe OD: 0 in · Soil: Common earth / loam
| Line item | Quantity | Notes |
|---|---|---|
| Spoil — bank | 29.63 yd³ | In-place (neat-line) dig volume |
| Spoil — loose haul | 37.04 yd³ | Includes 25% swell |
| Bedding material | 3.7 yd³ | 6" bedding, neat in-place volume |
| Backfill zone | 25.93 yd³ | Trench − bedding − pipe displacement |
Volumes are neat-line trench geometry only — they exclude OSHA sloping/benching over-dig and shoring. OSHA 1926 Subpart P governs. See the NORDIX excavation reference charts. Swell for Common earth / loam is a typical planning figure — swell 25% (typ 15–30%), shrink 10% (typ 5–15%); confirm with a geotech.
Trench safety governs the real dig. These are neat-line volumes only — they exclude the over-dig from OSHA sloping or benching and the working room for shoring or a trench box. Under OSHA 1926 Subpart P, an excavation 5 ft or deeper requires a protective system evaluated by a competent person, and laid-back slopes in weaker soils can more than double the dirt moved versus a vertical-wall neat line. See the OSHA trench slope chart for the maximum allowable slopes by soil type.
How this calculator works
Everything is box-and-cylinder geometry on the trench section, with the swell factor applied to the spoil you haul:
spoil = W × D × L ÷ 27 · bedding = W × bed depth × L ÷ 27 · backfill = spoil − bedding − π(OD/2)² × L ÷ 27
The pipe-displacement deduction matters more than it looks: a 6" pipe removes about 0.73 yd³ of backfill per 100 ft of run, and ordering backfill without the deduction leaves material on site. The loose-spoil line multiplies bank volume by (1 + swell%) — swell is an empirical, ranged soil property (typ 5–65% across the presets here), so treat the haul number as a planning figure and confirm the factor with a geotech where truck counts are contractual.
Worked example
A 24" wide × 48" deep trench, 100 ft long, with 6" of bedding in common earth (25% swell), no pipe deduction:
- Spoil: 2 × 4 × 100 = 800 ft³ ÷ 27 = 29.63 yd³ bank, hauling as 29.63 × 1.25 = 37.04 yd³ loose.
- Bedding: 2 × 0.5 × 100 = 100 ft³ ÷ 27 = 3.7 yd³ of stone or sand.
- Backfill zone: 800 − 100 = 700 ft³ ÷ 27 = 25.93 yd³. Add a 6" pipe and the deduction drops it to 25.2 yd³.
Enter the same run above (24 × 48 × 100, 6" bedding, common earth) to reproduce it, then set Pipe OD to 6 to see the displacement deduction.
Reference: spoil per 100 ft of trench
Neat-line spoil for common trench sections, computed by the same engine — bank yards dug and loose yards hauled at the common-earth 25% swell default (a typical planning figure, typ 15–30%). No bedding deducted; OSHA sloping/benching over-dig not included.
| Trench (W × D) | Spoil, bank (yd³/100 ft) | Spoil, loose @ 25% (yd³/100 ft) |
|---|---|---|
| 12" × 24" | 7.41 | 9.26 |
| 18" × 36" | 16.67 | 20.83 |
| 24" × 48" | 29.63 | 37.04 |
| 30" × 60" | 46.3 | 57.87 |
| 36" × 72" | 66.67 | 83.33 |
Frequently asked questions
How do I calculate trench spoil?
Multiply trench width by depth by length for the neat bank volume (cubic feet divided by 27 gives cubic yards), then apply a swell factor to get the loose volume the spoil actually occupies. This calculator reports both: the bank yardage you dig and the loose yardage you handle and haul. Width, depth, and bedding are entered in inches; length in feet.
Why is the spoil pile so much bigger than the trench?
Swell. Excavated soil bulks roughly 5–30% over its bank volume for typical soils and 40–65% for blasted rock — the ranges vary with material and moisture, and this calculator applies a mid-range default for the soil type you pick. A trench that computes to 30 bank yards can easily put 37+ loose yards on the ground, so plan casting room accordingly — and keep spoil at least 2 feet back from the trench edge per OSHA 1926.651.
Does the calculator subtract the pipe volume from the backfill?
Yes. The backfill zone is the total trench volume minus the bedding layer minus the cylinder displaced by the pipe OD you enter (leave OD at 0 for no deduction). Note that result is the neat in-place volume of the zone — if you are importing backfill, order more loose material than that, roughly the zone volume × (1 + swell) ÷ (1 − shrink) for the material, to end up compacted at grade.
How much bedding does a pipe trench need?
This calculator figures bedding as trench width × the bedding depth you enter × the run length. A 4–6 inch layer under the pipe is a common starting point, but the pipe manufacturer and project spec govern. Many specs also require select embedment from the bedding up past the pipe crown — this tool counts everything above the bedding layer as backfill zone, so if the spec calls for stone embedment, price part of that zone as imported stone rather than native backfill.
Do I have to haul away all the trench spoil?
Usually not. If the native material is suitable and the spec allows reuse, the backfill zone gets refilled from the spoil pile, and what you export is roughly the spoil that no longer fits — the volume displaced by bedding and pipe, plus the extra bank yardage compaction consumes. Compare the bank spoil and backfill lines from this calculator to bracket the surplus, and confirm reuse suitability with the geotech or inspector before assuming the native material can go back in.
At what depth does a trench need shoring or sloping?
OSHA 1926 Subpart P requires a protective system — sloping, benching, shoring, or a trench box — in any trench 5 feet or deeper, and in shallower trenches when there is any indication of a potential cave-in. Selecting the system depends on soil classification and site conditions, which is a competent-person call made in the field, not something to take from a volume calculator. Remember that protection changes geometry: boxes add trench width and sloping adds width at grade, both of which increase the spoil volume beyond the neat numbers here.
Method: neat-line trench geometry — W × D × L for spoil, W × bedding depth × L for bedding, and backfill = trench − bedding − pipe displacement (π r² L), all ÷ 27, with bank → loose spoil at the selected swell factor. Volumes exclude OSHA 1926 Subpart P sloping/benching over-dig, shoring working room, bell holes, and unsuitable-material over-excavation — the protective system a competent person selects governs the real quantities, and utility locates (811) come before any dig. Swell factors are typical planning ranges; confirm with a geotech.
Pair with the OSHA trench slope chart and trench protective systems reference for the safety side, the Excavation Volume Calculator for pads and mass ex, or the Soil Swell & Shrink Calculator for the volume-state conversions on their own.