Calculator inputs
Example data table
| Scenario | Length | Width | Lowering depth | Working space | Swell | Waste |
|---|---|---|---|---|---|---|
| Typical interior lowering | 9.00 m | 7.00 m | 0.60 m | 0.00 m | 25% | 5% |
| With perimeter trench | 30.00 ft | 22.00 ft | 2.00 ft | 0.50 ft | 30% | 8% |
| With pits and interior trenches | 10.00 m | 8.00 m | 0.75 m | 0.20 m | 20% | 5% |
Formula used
- Vertical sides: V = (L + 2A) × (W + 2A) × D
- Sloped sides (frustum approximation):
Bottom area A₂ = Lb × Wb, top area A₁ = (Lb + 2sD) × (Wb + 2sD)
Volume V = D/3 × (A₁ + A₂ + √(A₁A₂)), where s is the horizontal-to-vertical slope ratio. - Trenches: V = length × width × depth
- Swell: V_loose = V_in-situ × (1 + swell%)
- Waste: V_final = V_loose × (1 + waste%)
- Truckloads: loads ≈ V_final ÷ capacity
How to use this calculator
- Choose your unit system and enter basement length and width.
- Enter the lowering depth directly, or set existing and target depths.
- Add working space only if the excavation expands beyond the basement footprint.
- Enable optional trenches or pits if they are part of the scope.
- Set swell and waste to match your soil and handling method.
- Click Calculate to see results above the form.
- Use the CSV/PDF buttons to download a quick report.
Scope and measurement boundaries
This calculator separates in‑situ excavation from loose hauled material. Start with the basement plan dimensions and confirm whether the work stays inside existing foundation walls. Use working space only when access, shoring, or formwork expands the footprint beyond the slab line. Optional trenches and pits are added as discrete volumes, helping you match scope items in a bill of quantities.
Depth selection and verification
Basement lowering is often defined by either a single lowering depth or by an existing-to-target depth change. Field checks should include slab thickness, subgrade elevations, and any localized low points. When target depth is set, the calculator applies the difference to avoid double counting. If the depth varies, run multiple scenarios and average by area percentage for a defensible estimate.
Side slope assumptions for open excavation
For open cuts, sloped sides can significantly increase excavated volume. The model treats the excavation as a rectangular frustum where top dimensions expand by 2 × slope × depth. This approach is suitable for planning and bidding, but it should be adjusted if benching, stepped cuts, or irregular property lines constrain the excavation geometry.
Swell, waste, and hauling quantities
In‑situ soil expands when excavated; swell commonly ranges from 10–35% depending on soil type and handling. Waste allowances cover trimming, overbreak, and cleanup and are typically 3–10%. The calculator applies swell first, then waste, producing a final loose volume for haul planning. Enter truck capacity in m³ or yd³ to estimate loads and coordinate disposal logistics.
Documentation and audit-ready reporting
The downloadable CSV and PDF summarize inputs, assumptions, and outputs in a consistent format. Keep copies with soil reports, shoring notes, and site constraints so reviewers can trace the basis of quantity. When scope changes, update only the affected options—such as added trenches or revised waste—and re-export. This supports transparent comparisons across bids, change orders, and production tracking.
FAQs
1) Should I use working space for an interior-only lowering?
Usually no. If excavation remains inside existing walls, set working space to zero. Add it only when the footprint expands for access, shoring, formwork, or drainage details outside the basement outline.
2) What is the difference between in-situ and loose volume?
In-situ is the soil volume before excavation. Loose volume is the expanded material after digging. Swell converts in-situ to loose for hauling and disposal planning.
3) When should I choose sloped sides?
Select sloped sides for open excavations where sidewalls cannot remain vertical. Use a realistic horizontal-to-vertical ratio based on soil conditions and safety requirements, then validate with the shoring plan.
4) How do I account for varying lowering depths across the basement?
Run separate calculations for each depth zone and multiply each result by its area proportion. Add the weighted volumes together for a practical composite estimate.
5) Are trenches and pits included in the main volume?
No. The main volume covers the primary excavation prism or frustum. Trenches and pits are added as separate components so you can match them to specific scope lines and adjust them independently.
6) How accurate are the truckload estimates?
Truckloads are an approximation based on final loose volume and entered capacity. Real loads vary with moisture, compaction, and loading practices. Use this figure for planning, then refine with field production data.