Earthwork Volume Calculator
Calculate excavation volume for a pit, trench or basement, with optional sloped sides, then convert it to loose volume and truck loads.
How the calculator works
For vertical sides the volume is simply length × width × depth. With sloped sides, the top is larger than the bottom, so the calculator uses the exact volume of a pit with a rectangular base and uniform side slope s (horizontal run per unit of depth):
V = D × (L × W + s × D × (L + W) + (4 ÷ 3) × s² × D²)
This is the volume in its natural, undisturbed state (bank volume). Excavated soil takes up more room, so loose volume is V × (1 + swell). Truck loads are the loose volume divided by truck capacity, rounded up.
Worked example: pit 10 m × 6 m at the bottom, 2 m deep, 0.5:1 slopes
- Bottom area: 10 × 6 = 60 m²
- Slope term: 0.5 × 2 × (10 + 6) = 16
- Corner term: (4 ÷ 3) × 0.25 × 4 = 1.33
- Bank volume: 2 × (60 + 16 + 1.33) = 154.7 m³
- Loose volume at 25% swell: 154.7 × 1.25 = 193.3 m³
- With 10 m³ trucks: 20 loads
- Top size: (10 + 2 × 0.5 × 2) × (6 + 2 × 0.5 × 2) = 12 m × 8 m
Typical swell by soil type
| Soil | Swell on excavation | Common safe side slope (H:1) |
|---|---|---|
| Sand, gravel | 10-15% | 1.5 or flatter |
| Loam, common earth | 20-30% | 1 to 1.5 |
| Clay | 30-45% | 0.75 to 1 |
| Hard rock, blasted | 50-60% | Vertical to 0.25 |
Slopes depend on soil, groundwater, depth and local safety rules. Pits deeper than about 1.2 to 1.5 m usually need sloping, benching or shoring. Confirm with a geotechnical engineer and your local regulations.
Frequently asked questions
What is the difference between bank, loose and compacted volume?
Bank volume is soil in its natural state. Loose volume is the same soil after digging, which is larger because of air voids. Compacted volume is the soil after it is placed and compacted, which can be slightly smaller than bank volume.
Which volume do I use to order trucks?
Use loose volume, because that is what actually sits in the truck body. Bank volume is used to price excavation.
Does this work for trenches?
Yes. Enter the trench length, the bottom width and the depth. If the sides are vertical, set the side slope to 0.
How do I calculate backfill?
Subtract the volume of the structure placed below ground from the excavation volume to get the bank volume to backfill, then allow for compaction and swell when ordering imported fill.
Is this accurate enough for contract quantities?
It is a good estimate for uniform pits. Sloping ground, benched sides and varied depth need cross-section or survey-based methods, so treat this as a planning figure.
