Example data table
| Scenario | Shape | Dimensions | Total depth | Swell | Loose volume | Truckloads (6 m³) |
|---|---|---|---|---|---|---|
| Garden path | Rectangle | 10 m × 1.2 m | 0.20 m | 1.20 | 2.88 m³ | 0.48 |
| Round planter base | Circle | 2.5 m diameter | 0.15 m | 1.25 | 0.92 m³ | 0.15 |
| Two beds combined | Multi | (4×1.5) + (3×1.2) m | 0.25 m | 1.30 | 3.12 m³ | 0.52 |
Formula used
- Area (rectangle) = (L + 2Ws) × (W + 2Ws)
- Area (circle) = π × ( (D + 2Ws) / 2 )²
- Total depth = Topsoil depth + Subgrade depth
- Bank volume = Area × Total depth
- Bank + waste = Bank volume × (1 + Waste%/100)
- Loose volume = (Bank + waste) × Swell factor
- Compacted fill estimate ≈ (Bank + waste) ÷ Shrink factor
- Truckloads ≈ Loose volume ÷ Truck capacity
- Disposal mass ≈ Loose volume × Soil density
How to use this calculator
- Select your unit system and the shape of the excavation area.
- Enter dimensions, then add optional working space for clearance.
- Set topsoil strip and subgrade depth to get total cut depth.
- Adjust waste, swell, and shrink for your soil conditions.
- Press Calculate to see results above the form.
- Use Download CSV or Download PDF to keep records.
Project planning value for garden subgrades
Accurate subgrade excavation estimates prevent over-ordering base material and reduce disposal costs. This calculator converts your planned footprint and cut depth into bank volume, then applies allowances that reflect real garden work, including trimming, edge clean-up, and soil behavior after digging.
Understanding bank, loose, and compacted volumes
Bank volume represents soil in place before excavation. Loose volume increases after digging because voids expand; the swell factor captures this change. If you plan to reuse excavated soil as backfill, the shrink factor estimates the compacted volume needed to achieve a firm finished grade.
Working space and multi-section layouts
Garden beds and paths often require clearance for edging stones, formwork, or tool access. Working space is added to every side of the footprint, increasing calculated area consistently. For irregular layouts, the multiple-rectangle option totals several segments to approximate curved paths and stepped beds.
Hauling and handling productivity metrics
Loose volume connects directly to logistics. Truckloads provide a quick disposal or delivery benchmark, while wheelbarrow loads help estimate labor time for small sites. Pair the hauling values with access limitations, travel distance, and dump fees to build a realistic schedule and budget.
Quality checks for reliable results
Verify dimensions in one unit system before calculating. Use conservative waste and swell values when soil is wet or highly organic. If the project includes slopes, terraces, or varying depths, break the area into sections and calculate separately to avoid underestimating excavation.
FAQs
What depth should I enter for subgrade excavation?
Enter the planned cut below the finished surface to reach your base or structural layer. Include any extra depth required for drainage stone, root barriers, or leveling, then keep topsoil stripping separate.
Why does loose volume exceed bank volume?
Soil expands when excavated because it loses compaction and gains air voids. The swell factor models this behavior, which is important for hauling, staging, and estimating disposal capacity.
When should I use the waste allowance?
Use waste allowance for trimming, uneven edges, and small over-excavations during shaping. For tight garden features, 5–10% is common; use higher values for rocky ground or manual digging.
How do I estimate truck capacity if I only know yards?
Select yd³ as the truck unit and enter the capacity from your contractor or rental listing. The calculator converts it internally and returns both metric and yard-based volumes for comparison.
Can I combine different shapes in one calculation?
Use multiple rectangles to combine segments and approximate mixed shapes. For a separate circular feature, run another calculation and add totals to create a complete site excavation plan.
Is the disposal mass estimate exact?
No. Mass depends on moisture and soil type. The density input provides a practical estimate for planning limits, fees, or transport constraints; adjust density when you have site-specific test data.