Earthwork Calculator
Enter pit dimensions and slope ratio to get cut volume, backfill and spoil to remove.
Quick answer
With the default inputs: Excavation type Rectangular pit · Bottom length 10 · Bottom width 6 etc.Cut volume 231.4 m³
Edit the inputs below to recalculate.Inputs
Result
Cut volume
231.4m³
| Method | Pit |
| Top dimensions | 12.0 × 8.0 m |
| Cut (bank) | 231.4m³ |
| Less structure | 30.0m³ |
| Backfill (compacted) | 201.4m³ |
| Bank soil needed (0.90 compaction) | 223.8m³ |
| Spoil off-site (bank) | 7.6m³ |
| Spoil (loose) | 9.9m³ |
| Trucks @15 m³ | 1loads |
Slope ratios follow the earthwork code. Final values depend on soil, groundwater and the shoring design.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
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.
How to work it out
- Fix the base dimensions, then add working space: 300-500 mm each side for concrete footings, 500-800 mm where formwork or brickwork needs access, more again for waterproofing.
- Set the batter. Class 1-2 soils use 1:0.33, class 3 1:0.5, class 4 1:0.75. Beyond 5 m depth, or next to existing structures, battering is not acceptable and shoring is required.
- Excavation with four battered sides: V = (a+KH)(b+KH)H + K²H³/3, where a and b include working space.
- Backfill = excavation − the volume of structure left buried (footings, blinding, basement). Without that deduction the backfill is overstated.
- Disposal = excavation × (1 + bulking factor) − backfill. Bulking is 1.2-1.3 for classes 1-2, since loose soil occupies more than intact ground.
Where it goes wrong
- Confusing the batter ratio with a gradient — 1:0.33 means K = 0.33, while 33% is the gradient; substituting 33 makes the volume a hundred times too large.
- Omitting working space — digging to the footing outline leaves no room to fix steel or erect formwork, and the second dig costs double.
- Not deducting the buried structure — a 10 × 6 × 3 m pit with a 30 m³ footing means buying and carting away 30 m³ of soil for nothing.
- Ignoring bulking on disposal — 1 m³ intact becomes 1.2-1.3 m³ loose, so trucks booked by intact volume will not fit it and haulage is under-costed by 20%.
Material and cost
Machine excavation 8-25 CNY/m³ including loading; hand digging 40-80. Disposal 15-40 CNY/m³ including tip fees, rising beyond 10 km. Placing and compacting backfill 15-30 CNY/m³.
On site
- Take the batter per layer where soils differ; a soft layer over hard cannot be averaged to 0.33.
- Any pit deeper than 5 m, or with a structure or service within one depth of the crest, needs a designed support system rather than a batter.
- In cold regions leave 300 mm of protective soil over the formation and remove it just before backfilling.
Basis
- GB 50854-2013 Code for measurement of building and decoration works, Appendix A
- GB 50202-2018 Code for acceptance of foundation construction
- JGJ 120-2012 Technical specification for retaining and protection of building excavations
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.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Earthwork Calculator. 2026-10-25. https://jianzhujisuan.com/en/earthwork
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.