How to Calculate Excavation Volume
Length × width × depth for simple cuts, sectioned for sloped or irregular ground
The base formula
For a simple, uniform-depth cut, excavation volume is length × width × depth, exactly like a concrete slab — the difference is you're calculating material to remove, not material to place.
Handling varying depth
Sloped ground or a stepped foundation means depth isn't constant across the excavation. Split the area into sections of roughly uniform depth and calculate each separately, or use an average depth across the whole area for a rough estimate — sectioning is more accurate for significant slope.
Bulking factor
Soil expands when it's dug up and loosened — a phenomenon called bulking or swell. This means the volume of loose, excavated soil you need to haul away is larger than the in-place (bank) volume you calculated, often by 15-30% depending on soil type. This matters for estimating truck loads or disposal costs, and is separate from the excavation-volume calculation itself.
Worked Example
A basement excavation, 30 ft × 40 ft, 8 ft deep.
In-place (bank) volume: 30 × 40 × 8 = 9,600 ft³ = 355.6 yd³
With an estimated 20% bulking for hauling: 355.6 × 1.20 ≈ 427 yd³ (loose volume)
Assumptions & Limitations
- Bulking factors vary significantly by soil type (clay, sand, rock) — use a figure appropriate to your actual soil, or consult a local excavation contractor.
Related Calculators
Related Guides
Sources
NIST SP 811
Unit conversion reference (cubic feet, cubic yards, cubic metres).
NIST SP 811 — reference