Excavation & Earthwork Calculator
Volume of pits, trenches with side slope and round pits, with bulking and truck trips.
Free tool by EngineeringNepal.com.np · Results are for guidance; check critical figures with a qualified engineer.
Excavation volume for foundations
Earthwork in excavation is usually the first item in a building or road estimate. Payment is made on the solid (in-situ) volume measured in the ground, but trucks carry the loosened soil, which takes 15 to 50% more space. This calculator gives both, plus the number of truck or tractor trips needed to remove the spoil.
Formulas
- Rectangular pit: V = length × width × depth. Isolated column footings are usually dug as square pits a little larger than the footing to leave working space.
- Trench with side slope: cross-section area = (b + s·d) × d, where b is bottom width, d is depth and s is horizontal per 1 vertical. Top width = b + 2·s·d.
- Round pit (soak pit, well): V = π/4 × D² × depth.
Frequently asked questions
What side slope should I use?
Firm soil can stand nearly vertical for shallow depths, while loose or wet soil needs 1:1 or flatter. For trenches deeper than 1.5 m, provide shoring or safe slopes to protect workers.
What is a normal truck capacity?
A small tractor trolley carries around 80 to 100 cft, and tippers commonly carry 250 to 500 cft depending on size. Enter the figure used by your supplier.
How to use the excavation calculator
- Pick the shape: Rectangular pit for column footings, Trench / side slope for wall footings, drains and pipe lines, or Round pit for soak pits and wells.
- Choose metres or feet, then enter the number of identical pits or trenches.
- Enter the pit size including working space, not the footing size. Depth is from natural ground level to the bottom of the PCC bed.
- Pick the soil type for bulking and enter your truck or tractor capacity in cft. Add a rate per m³ if you want a cost.
Worked example 1: footing pits for a 12-column house
Each footing in our isolated footing quantity example is 1.5 × 1.5 m with 0.3 m working space on each side, so the pit is 2.1 × 2.1 m and 1.5 m deep. In Rectangular pit mode with 12 pits, ordinary soil (25%) and a 100 cft tractor:
- Excavation = 2.1 × 2.1 × 1.5 × 12 = 79.38 m³ (2,803 cft)
- Loose soil after bulking = 79.38 × 1.25 = 99.23 m³, which is 36 tractor trips (9 trips with a 400 cft tipper)
- At Rs 529 per m³ (manual excavation in ordinary soil in the Suryabinayak Municipality rate analysis for 2081/82), the cost is about Rs 41,992
Most of that soil goes back as backfill once the footings are cast. In the footing example, backfill is 5.61 m³ of each 6.615 m³ pit, so only about 12.06 m³ solid (15.1 m³ loose, about 532 cft) is surplus, or 6 tractor trips. Keep the rest on site if there is space.
Worked example 2: trench for a boundary wall footing
A 30 m trench, 0.9 m wide at the bottom and 1.2 m deep, in soil that needs a 0.5 : 1 side slope. In Trench mode: area = (0.9 + 0.5 × 1.2) × 1.2 = 1.8 m², volume = 1.8 × 30 = 54.00 m³, top width 2.1 m. With vertical sides (slope 0) the same trench is only 32.40 m³, so the slope adds 67% more digging. That is why shoring is often cheaper than sloping in deep trenches on tight plots.
Worked example 3: soak pit
A round soak pit 1.5 m in diameter and 3.0 m deep in hard soil (35%): π/4 × 1.5² × 3.0 = 5.30 m³, 7.16 m³ loose, 3 tractor trips. At the same rate book's hard soil rate of Rs 634.80 per m³, about Rs 3,365.
Bulking and truck trips per 10 m³ dug
| Soil (bulking) | Loose volume | Trips, 100 cft tractor | Trips, 400 cft tipper |
|---|---|---|---|
| Sandy soil (15%) | 11.5 m³ (406 cft) | 5 | 2 |
| Ordinary soil (25%) | 12.5 m³ (441 cft) | 5 | 2 |
| Hard / clayey soil (35%) | 13.5 m³ (477 cft) | 5 | 2 |
| Rock (50%) | 15.0 m³ (530 cft) | 6 | 2 |
Rates in the table and examples are one municipality's published rates for public works in one year. Check your own municipality's rate book, and agree with the contractor whether excavation is paid on solid or loose volume before work starts.
Common mistakes
- Paying on loose volume. Earthwork is measured and paid on the solid volume in the ground. The loose figure is only for haulage.
- Using the footing size as the pit size. Without working space, workers cannot fix formwork and the pit sides fall into the concrete.
- Measuring depth from road or plinth level. Take depth from natural ground level as recorded before digging. Note the ground levels at each pit corner.
- Counting overlap twice. Where two pits or a pit and a trench overlap, deduct the shared part once.
- No support in deep cuts. Trenches deeper than about 1.5 m in loose or wet soil need shoring or a safe slope. Keep spoil at least 0.6 m back from the edge.
- Hauling away soil that is needed for backfill. Plan the surplus from the backfill quantity first.
Frequently asked questions
How many cft in 1 m³ of excavation?
1 m³ = 35.31 cft. The site's m³ to cft guide has a full table.
Does the calculator include backfill?
No. Backfill is excavation minus the PCC, footing and column stub below ground. Work it out from your footing quantities, then the surplus is what you haul away.
What soil type should I choose if I do not know?
Use ordinary soil (25%) for a first estimate, and change it once the first pit is open. For a full budget, see the house construction cost estimator.
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