Excavation Calculator
Calculate how much dirt you will dig out of a pad, basement, trench, set of post holes or sloped pond. You get bank and loose cubic yards, soil weight, swell, the number of truckloads to haul it away, and how much fill you need to backfill.
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Excavation volume = length × width × depth (ft) ÷ 27 cubic yards. That is the bank volume. Dug soil swells, so multiply by 1.25 for common earth to get the loose volume you haul. A 40 × 30 ft pad dug 3 ft deep is 133 bank yd³, about 167 yd³ loose, or 17 tandem truckloads.
How to use this excavation calculator
- Pick the dig shape: rectangle, trench, round holes, or a sloped pit or pond.
- Enter dimensions. Trench width is in inches, and everything else in feet (or metres).
- Choose the soil type. It sets the swell factor and the weight.
- Choose the truck size to see haul-off loads, limited by volume or weight, whichever comes first.
- Check the backfill line if you are filling around a foundation or pipe afterwards.
Excavation volume formulas
| Shape | Volume (ft³) |
|---|---|
| Rectangle (pad, footing, basement) | Length × Width × Depth |
| Trench | Length × (Width in ÷ 12) × Depth |
| Round hole | π × (Diameter ÷ 2)² × Depth × number of holes |
| Sloped pit or pond (prismoidal) | Depth ÷ 3 × (Atop + Abottom + √(Atop × Abottom)) |
Divide cubic feet by 27 for cubic yards. For uneven ground, take depth readings on a grid and average them, or use the cut and fill calculator.
Bank, loose and compacted: soil swell and shrink
The same soil has three volumes. Bank is in the ground, loose is in the truck, and compacted is tamped back in place. You pay to dig bank yards, haul loose yards and buy fill to reach compacted yards.
| Soil | Swell (bank → loose) | Approx. bank weight per yd³ | Loose yd³ per 10 bank yd³ |
|---|---|---|---|
| Sand, gravel | 12–15% | ~3,000 lb | 11.5 |
| Common earth, loam | ~25% | ~2,600 lb | 12.5 |
| Topsoil | ~30% | ~2,500 lb | 13.0 |
| Clay | 30–40% | ~2,800 lb | 13.5 |
| Rock, blasted or broken | 50–60%+ | ~4,000 lb | 15.0 |
Weights vary a lot with moisture. Wet clay is far heavier than dry, so for big jobs ask the hauler how they charge, by load or by ton.
Trench volume per foot
| Trench (width × depth) | Typical use | ft³ per foot | Feet per yd³ |
|---|---|---|---|
| 6 × 18 in | Irrigation, low-voltage | 0.75 | 36 |
| 12 × 24 in | French drain, small footing | 2.0 | 13.5 |
| 18 × 36 in | Drain or utility line | 4.5 | 6.0 |
| 24 × 48 in | Frost-depth footing, sewer | 8.0 | 3.4 |
Before you dig
- Call 811 (US) a few days aheadUtility locates are free, and hitting a gas or power line is deadly and expensive.
- Trenches 5 ft or deeper need protectionOSHA requires sloping, shoring or a trench box unless the trench is in stable rock. Soil weighs over a ton per cubic yard.
- Leave working room around foundationsAdd 2–3 ft on each side for forms, waterproofing and drainage. That extra dirt is often 20–30% of the total.
- Plan where the spoil goesKeep piles at least 2 ft back from the edge. Loose soil takes up more space than you expect.
Worked examples
- Basement 30 × 40 ft, 8 ft deep
- 9,600 ft³ = 355.6 bank yd³
- Common earth swells 25%
- 444 loose yd³
- Tandem loads (~10 yd³)
- 45 loads
- Pond: top 30 × 20 ft, bottom 20 × 10 ft, 4 ft deep
- 4 ÷ 3 × (600 + 200 + 346) = 1,528 ft³
- Bank volume
- 56.6 yd³
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Frequently asked questions
How do I calculate excavation volume?
Length × width × depth in feet ÷ 27 = bank cubic yards. For sloped sides: depth ÷ 3 × (top area + bottom area + √(top × bottom)).
What is the swell factor of soil?
About 12–15% for sand and gravel, 25% for common earth, 30–40% for clay and 50%+ for broken rock.
How many truckloads of dirt will I need to haul?
Loose volume (bank × (1 + swell)) ÷ truck capacity. A tandem dump carries about 10 loose yd³, but heavy soil can hit the weight limit first.
How much does a cubic yard of dirt weigh?
Roughly 2,000–2,700 lb for common earth, about 2,800 lb for clay and around 3,000 lb for sand and gravel in the bank.
How much fill do I need to backfill a hole?
About 15–25% more loose fill than the hole volume, because it compacts as you tamp it in lifts.
How deep can I dig a trench without shoring?
Under OSHA, trenches 5 ft or deeper need a protective system unless they are in stable rock. Shallower trenches still need checking for cave-in risk.
What this calculator assumes
- Swell factors and weights are typical values. Actual figures depend on moisture and how the soil was laid down.
- Truckloads are limited by whichever is reached first, loose volume or about 1.4 tons per yd³ of capacity.
- Backfill assumes about 20% extra for compaction, using fill dirt at about 1 ton per yd³.
- Planning estimates only. Excavation near structures, slopes or utilities needs a qualified contractor.