Excavation & Trench Volume Calculator
Bank volume of trenches and pits with vertical or sloped sides, loose volume from your swell factor, truck loads from your body capacity, and backfill.
How much soil comes out, how much bigger it gets on the truck, how many loads that is, and how much goes back — from the trench section and the factors you supply.
Example: A 30 m trench, 0.6 m wide at the bottom, 1.2 m deep with 0.5:1 sides is 1.8 m wide at the top: 43.2 m³ in the bank, 54 m³ loose at 25 % swell — seven 8 m³ truck loads.
Bank, loose, backfill:
three volumes, one hole.
The trench section, why dug soil takes more room, and what the truck-load count assumes.
The trench section
A trench with battered sides is a trapezoid in cross-section: the top width is the bottom width plus twice the depth times the side slope (given as horizontal run per unit of rise — 0 for vertical sides, 0.5 for 1 in 2, 1 for 45°). The section area is the average of the two widths times the depth, and the bank volume is that area times the length, times the number of identical trenches. Several trenches or pits can be listed and are summed. Ground that slopes along the trench, or a trench that changes depth, is better entered as two or three segments with their own depths.
Swell and loose volume
Soil in the ground is compact; once dug it bulks up, so the volume to haul away is larger than the hole. The swell factor depends on the material — sand, clay, rock and topsoil all differ, and so does the digging method — so it is an input, and leaving it at zero is flagged rather than filled with a guess. Take the figure from your own experience with the soil, the contractor, or a site investigation report. Compaction of returned fill (shrinkage) is the reverse effect and is not applied here.
Truck loads and backfill
Loads are the loose volume divided by the truck body capacity you enter, rounded up: struck capacity, heaped capacity and the legal payload by weight are different limits, so use the one your haulier works to. Backfill is the bank volume minus whatever stays in the excavation — pipe, bedding, foundations, duct — entered as a volume; the imported fill needed to replace it depends on its own compaction and is not computed.
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SOURCES
- Prismoidal / trapezoidal end-area method for earthwork volumes — standard surveying practice (e.g. Ghilani & Wolf, Elementary Surveying, chapter on volumes)
- NIST Special Publication 811 (2008), Guide for the Use of the SI — cubic yard 0.764 554 857 984 m³
Last reviewed 19 September 2026. How results are checked: How we verify.