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.
Divide cubic feet by 27 to get bank cubic yards (BCY): the volume of soil as it sits undisturbed in the ground.
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.
Swell: dug soil takes up more room
Soil loosens when it is dug and takes up more space than it did in the ground. Earthmoving references describe three states: bank (in place), loose (after digging) and compacted. The U.S. Army and Marine Corps earthmoving manual (TM 3-34.62) expresses swell as a percentage increase: dry clay typically swells about 40%, so 1 cubic yard of clay in the ground fills about 1.4 cubic yards once dug.
Loose volume = bank volume × (1 + swell). The Excavation Calculator applies a default swell for the soil type you pick, and you can change it.
| Material | Typical swell |
|---|---|
| Sand or gravel (dry or wet) | 10–15% |
| Earth (loam or silt), dry | 15–35% |
| Earth (loam or silt), wet | 25% |
| Clay (dry or wet) | 40% |
| Trap rock | 50% |
| Shale (soft rock) | 65% |
Hauling: size trucks on loose volume
Trucks and containers are filled with loose soil, so divide the loose volume by the truck's capacity and round up. Heavy material such as gravel can reach a truck's weight limit before it is full, so check the payload as well.
Backfill: compacted soil takes less room
Soil put back and compacted takes up less space than it did in the ground. TM 3-34.62 gives bank-to-compacted factors of 0.95 for sand or gravel and 0.90 for loam or clay, so 10 bank cubic yards of loam compacts to about 9 cubic yards. Use this to check whether the excavated soil will cover a backfill.
Safety in deeper excavations
Under OSHA's construction rules (29 CFR 1926.652), workers in an excavation must be protected from cave-ins by a protective system. The exceptions are an excavation made entirely in stable rock, or one less than 5 ft deep where a competent person finds no indication of a potential cave-in.
Worked Example
A basement excavation, 30 ft × 40 ft, 8 ft deep, in common earth (loam), hauled in 10 yd³ trucks.
Bank volume: 30 × 40 × 8 = 9,600 ft³ ÷ 27 = 355.6 yd³
Loose volume at 25% swell (the Excavation Calculator's common-earth default; TM 3-34.62 lists 25% for wet loam): 355.6 × 1.25 = 444.4 yd³
Truck loads: 444.4 ÷ 10 = 44.4 → 45 loads
Assumptions & Limitations
- Swell figures are averages; use a figure for your actual soil, or one from a local excavation contractor.
FAQ
- What is the swell factor for soil?
- It is the percentage increase in volume when soil is dug out. TM 3-34.62 lists about 10–15% for sand or gravel, 15–35% for dry loam, 25% for wet loam and 40% for clay.
- How many truckloads will my excavation be?
- Multiply the bank volume by 1 plus the swell to get the loose volume, then divide by the truck's capacity and round up. 355.6 bank cubic yards of loam at 25% swell is 444.4 loose cubic yards, or 45 loads of 10 cubic yards.
- What is the difference between bank, loose and compacted volume?
- Bank volume is the soil as it sits in the ground, loose volume is the same soil after digging, and compacted volume is after it has been placed and compacted. Loose is the largest; for soil and gravel, compacted is usually the smallest.
Related Calculators
Related Guides
Sources
NIST SP 811
Unit conversion reference (cubic feet, cubic yards, cubic metres).
NIST SP 811 — referenceTM 3-34.62/MCRP 3-40D.9, Earthmoving Operations (U.S. Army and Marine Corps, 2025)
Table 1-1 material volume conversion factors and Table 1-2 swell percentages (averages for common materials); paragraph 1-11 on swell.
TM 3-34.62/MCRP 3-40D.9, Earthmoving Operations (U.S. Army and Marine Corps, 2025) — reference29 CFR 1926.652, Requirements for protective systems
Protection from cave-ins and its exceptions (stable rock; under 5 ft with no indication of a potential cave-in).
29 CFR 1926.652, Requirements for protective systems — reference