Excavation Calculator

Excavation formula

Bank cu yd = Length (ft) x Width (ft) x Depth (ft) / 27
Loose cu yd = Bank cu yd x (1 + swell %)  (sand 12%, loam 25%, clay 35%, rock 50%)
Tons = Bank cu yd x density  (sand 1.5, loam 1.4, clay 1.5, rock 2.0 tons per bank cu yd)
Truckloads = Loose cu yd / truck capacity, rounded up

Worked example

A 40 x 25 ft basement dug 8 ft deep in clay, hauled in 14 yard tri-axles at $15 per loose yard: bank volume is 40 x 25 x 8 = 8,000 cubic feet, or 8,000 / 27 = 296.3 cubic yards. Clay swells 35%, so the loose volume is 296.3 x 1.35 = 400 cubic yards. Weight is 296.3 x 1.5 = 444.4 tons.

Truckloads: 400 / 14 = 28.6, so 29 loads. Haul-off cost is 400 x $15 = $6,000 before disposal fees. At 8 ft deep the walls must be sloped back or shored, which adds excavation volume beyond the footprint.

Quick reference

Bank, loose and compacted volume

Excavators quote digging by the bank cubic yard, the volume measured in the ground before it is disturbed. Once the bucket breaks it loose, air gets between the particles and the pile grows: sand and gravel by roughly 12 percent, loam by 25, clay by 35, and blasted rock by half again. Trucking and dump fees are charged on that loose volume, which is why a 67 yard hole produces 83 yards of loads.

If the soil is coming back as fill, the third number matters: compacted volume. Loam placed and compacted in lifts ends up about 10 percent smaller than it was in the bank, so a hole backfilled with its own spoil comes up short. Order extra fill or plan on the difference.

Before and during the dig

Call 811 or submit an online locate request at least two to three business days ahead; every state requires it and the utility marks are free. Private lines such as irrigation, gas to a grill, or power to a shed are not marked, so trace those yourself. Check setbacks from property lines, septic fields and footings, and figure out where the spoil pile will sit before the first bucket comes out.

Any excavation 5 ft or deeper falls under OSHA trenching rules: the walls must be sloped back, benched, or supported with a trench box or shoring, and a ladder within 25 ft of every worker. Sloping widens the top of the hole and adds volume, often 30 to 50 percent on a deep basement. Keep spoil and equipment at least 2 ft back from the edge, and never enter an unprotected trench, even for a minute.

Key facts

• Soil has three volumes: bank (undisturbed in the ground), loose (after digging, 12 to 50 percent larger), and compacted (after placement, often smaller than bank).
• Loam swells about 25 percent when excavated, so 100 bank cubic yards becomes 125 loose yards in the trucks.
• Call 811 at least two to three business days before digging; utilities mark their lines for free and it is the law in every state.
• OSHA requires a protective system (sloping, benching, shielding or shoring) for any trench 5 ft or deeper, and an engineered design at 20 ft or deeper.
• A tandem dump truck carries about 10 cubic yards, a tri-axle 14 to 16, and a semi end dump 18 to 22, limited by weight as much as volume.

Frequently asked questions

Sources and references

• •29 CFR 1926.652, Requirements for protective systems (OSHA)
• •Trenching and Excavation overview (OSHA)
• •811 Before You Dig (Common Ground Alliance)
• •NIST Handbook 44, Appendix C, General Tables of Units of Measurement (NIST)