Excavation Calculator: Dirt Volume, Swell & Truckloads

How do you calculate excavation volume?

Measure the hole, multiply length × width × depth, and you have the bank volume: the soil as it sits in the ground. Then multiply by 1 plus the swell percentage to get the loose volume that the excavator loads into trucks. The calculator does both and counts truckloads.

Bank volume (yd³) = length (ft) × width (ft) × depth (ft) ÷ 27
Loose volume (yd³) = bank volume × (1 + swell % ÷ 100)
Truckloads = loose volume ÷ truck capacity (loose yd³), rounded up

Bank, loose and compacted are the three states earthwork estimators track. Soil in the ground is dense. Digging breaks it up and lets air in, so the same soil takes more room in the bucket and the truck bed. Rolling it back into a trench squeezes it down again. The thesis we use for swell ranges (Crooks, Auburn University, 2013) notes that the factors depend on moisture content, density and soil type, which is why one number never fits every site.

For a round hole, use π × (diameter ÷ 2)² × depth instead of length × width. A 4 ft wide hole 4 ft deep is 50.27 ft³, or 1.86 bank yd³, and 2.42–2.79 loose yd³ in clay.

What is the swell factor of soil?

Swell is the percentage by which soil grows when it is dug. The only published ranges we could verify from a university or government source come from a 2013 Auburn University master’s thesis that compared state highway earthwork methods in the southeastern US. Its conclusions give these ranges:

Source: Crooks (2013), Auburn University, summary of findings. Loose-per-bank columns computed from the percentages.

The ranges are wide, and the thesis says why. It found that most southeastern state DOTs do not publish a guide to typical shrink and swell factors, and that the materials and test engineers assign factors to each project from soil tests. It also found the definition of rock has a large effect on earthwork numbers. So treat the table as a planning bracket. On a real job, the geotechnical report, the DOT plans or your excavator’s experience with local soil gives a better single number.

Which end of the range to plan for? For hauling, the high end is the safe side. One extra truck is cheaper than a crew waiting for a truck that was never booked. That is why the calculator’s headline number uses the top of the range unless you enter your own swell.

How many truckloads of dirt will I have?

Divide the loose volume by what your truck carries, then round up. The table below runs common residential digs through the clay range (30–50%) with a truck carrying 10 loose yd³. Change the truck size in the calculator to match your hauler.

Truck size changes the count more than anything else. The same basement at the 50% end needs 107 loads at 5 yd³, 54 at 10 yd³, 39 at 14 yd³ and 27 at 20 yd³. Ask your hauler two questions: how many loose yards the body holds, and what weight the truck is allowed to carry. Wet clay is heavy, and a truck can hit its legal weight before the bed is full.

The “10 yd³” truck in these examples is a round number for illustration, not a standard size. Use the capacity your hauler quotes.

What about sloped sides and uneven ground?

Real holes are rarely perfect boxes. For a pit with sloped sides, average the top and bottom areas and multiply by the depth. This is the average-end-area method, a quick approximation that earthwork estimators use. A pit 20 × 10 ft at the top and 14 × 4 ft at the bottom, 3 ft deep, works out to (200 + 56) ÷ 2 × 3 = 384 ft³, or 14.22 bank yd³. A straight-sided box with the top dimensions would have said 22.22 yd³, so the box estimate over-orders trucks by more than half.

For ground that slopes across the site, take depth readings at a grid of points (every 5 or 10 ft), average them, and use that average depth. For a pool or a pond with a deep end, use the average depth too.

Is it safe to dig a trench this deep?

Depth changes the rules, not just the volume. OSHA’s excavation standard (29 CFR 1926 Subpart P) sets these points for work sites in the US:

• 5 ft (1.52 m) and deeper: each worker in the excavation must be protected from cave-ins by a protective system (sloping, benching, shoring or a shield) unless the excavation is entirely in stable rock (1926.652(a)(1)).
• Less than 5 ft: a protective system is still required unless a competent person examines the ground and finds no indication of a potential cave-in.
• 4 ft (1.22 m) and deeper: trenches need a stairway, ladder, ramp or other safe way out, placed so no worker travels more than 25 ft (7.62 m) laterally to reach it (1926.651(c)(2)).
• Spoil piles: excavated material must be kept at least 2 ft (0.61 m) from the edge, or held back by retaining devices (1926.651(j)(2)). Plan where the loose soil from this calculator will sit.
• Utilities: the estimated location of sewer, telephone, fuel, electric, water and other underground lines must be determined before the excavation is opened (1926.651(b)(1)). In the US, call 811 before you dig.

OSHA rules apply to employers, but the soil does not care who is in the trench. A homeowner digging a footing trench in soft or wet ground faces the same cave-in risk. If your dig is deep or the walls look unstable, hire an excavation contractor.

Excavation volume in metric

The method is the same in metres: length × width × depth gives bank m³, then multiply by 1 + swell %.

1 yd³ = 0.7645549 m³ (NIST SP 811), so a 10 yd³ body holds about 7.65 m³. The calculator takes feet; for metric dimensions, multiply metres by 3.2808 or read the m³ lines in the results.

Bank, loose and compacted: how they fit together

Swell and compaction are opposite steps. Digging takes soil from bank to loose (it grows). Placing and rolling it takes it from loose to compacted (it shrinks again, often below the bank volume). The same Auburn thesis reported shrink ranges of 10–18% for clays, 11–35% for sands and 5–22% for rocky, gravelly soils, measured against bank volume.

This matters if you plan to reuse your own dirt. Spoil from a footing trench will not refill the trench once the concrete takes up space, and spoil from a pool dig can cover a lot of yard when spread loose. If you are buying soil in, the fill dirt calculator handles the compaction side. If you are hauling it out, use the loose number from this page.

Common excavation estimating mistakes

• Ordering trucks on bank yards. A truck carries loose soil. A 22 yd³ hole can fill 33 yd³ of truck beds.
• Using one swell number for every soil. Clay and sand behave differently, and even one soil type varies with moisture.
• Ignoring over-dig. Working room around forms and sloped walls change the volume. Measure the hole, not the drawing.
• Forgetting truck weight limits. Wet clay can max out a truck’s weight before its volume.
• Leaving no room for spoil. Piles must stay at least 2 ft back from the edge, and loose soil takes more space than you expect.
• Skipping the utility locate. Find buried lines before you open the ground.

All results are planning estimates. A soil report, your excavator’s swell figure and your hauler’s truck capacity give better numbers for your site.