Earthwork Calculator
Enter pit dimensions and slope ratio to get cut volume, backfill and spoil to remove.
Inputs
Result
Formula
| Rectangular pit (prismoid) | V = H/6 × [ab + (a+2mH)(b+2mH) + 4(a+mH)(b+mH)] |
| Trench | V = (B + mH) × H × L |
| Backfill | V_back = V_cut − structure volume |
| Loose volume | V_loose = V_spoil × 1.3 |
A 10×6 m pit 3 m deep with 1:0.33 batter and a 30 m³ structure: 231.4 m³ cut, 201.4 m³ of backfill once compacted, needing 223.8 m³ of bank soil — 7.6 m³ of spoil, 9.9 m³ loose, one 15 m³ truck load.
FAQ
How do I choose the slope ratio?
By soil type: 1:0.5 to 1:1 for sand and fill, 1:0.33 to 1:0.5 for silt and ordinary clay, 1:0.33 for stiff clay. Pits deeper than 5 m normally need shoring rather than battering, and any pit with groundwater above the base must be dewatered first.
What is the difference between bank, loose and compacted volume?
Bank volume is undisturbed soil and is the basis for measurement and payment. Loose volume is what it becomes after digging, about 1.25-1.35 times larger, and is what trucks are rated in. Compacted volume is smaller than bank volume, so backfill quantities are multiplied by roughly 1.15. Mixing these up doubles or halves your haulage cost.
Should working space be included?
Yes. Formwork and access need room, typically 300-800 mm on each side: 300 mm for formwork on concrete footings, 800 mm where a waterproof membrane is applied, plus more for drainage trenches. Enter bottom dimensions that already include working space.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.