Excavation & Trench Volume Calculator
Whether you are digging footings for an extension, a trench for a drainage run, or pier holes for a deck, the volume you dig is not the volume you haul away. Soil bulks up when it is loosened — a phenomenon called swell — so the loose spoil on the back of the truck takes up noticeably more room than the neat hole you measured on the ground.
This calculator turns your dimensions and a soil type into the three volumes that actually matter: bank (the in-situ cut you measure), loose (the swelled spoil you haul), and compacted (what the same material occupies once it is placed and rolled back down as fill). It also estimates spoil weight, the number of skip, dumpster or truck loads to shift it, and an optional cost — all in your browser, with nothing sent to a server.
Add a zone for each part of the job — a pad, a run of trenches, a set of pier holes — pick a soil preset or enter your own factors, and the results rail totals the whole excavation as you type.
How to use the excavation calculator
Choose metric or imperial units at the top; the calculator remembers your preference in your browser. Metric works in metres, cubic metres and tonnes, imperial in feet, cubic yards and short tons.
Open Soil & assumptions to pick a soil type. The bank density, swell percentage and shrinkage percentage fill in from the preset, but every one of them is editable — override them with your own site values or your engineer's figures when you have them.
Add a zone per distinct dig: choose its shape (pad / basement, trench, pier hole, or a direct volume), enter the dimensions, and set a count for repeated trenches or holes. The results rail accumulates every zone into one haul volume, weight, load count and cost.
How to calculate excavation volume in 5 steps
- Choose unitsSelect metric (m, m³, tonnes) or imperial (ft, yd³, short tons) at the top of the page.
- Pick a soil typeOpen Soil & assumptions and choose a preset, or select Custom and enter your own bank density, swell and shrinkage.
- Add zonesAdd one zone per dig. Choose a shape (pad, trench, pier hole or direct volume), enter the dimensions, and set a count for repeated trenches or holes.
- Set batter and backfill (optional)In a zone's Advanced panel, add a batter (side slope) to over-dig sloped walls, or enter a structure volume so the tool nets off backfill and shows spoil to export or borrow to import.
- Read the resultsThe rail shows loose haul volume, truck or skip loads (with the binding basis), bank vs compacted volume, spoil weight and optional cost.
Bank, loose and compacted volume — how the maths works
Earthwork tracks the same soil through three states, all referenced to the bank (in-situ) volume you measure in the ground.
Loose (haul) volume = bank volume × (1 + swell). Loosened soil bulks up: a cubic metre of common earth cut from the ground occupies roughly 1.25 m³ once it is dug and piled loose. This is the volume you order skips or trucks against, and getting the swell direction wrong is the single most common excavation-estimating mistake — it silently under-books your haulage.
Compacted volume = bank volume × (1 − shrinkage). When soil is placed back as fill and compacted, it settles to less than its original in-ground volume. This is what you need when you are backfilling a void to a finished level.
Spoil weight = bank volume × bank density. Mass is conserved across all three states — loosening and compacting change the volume, not the amount of material — so weight is always taken from the bank volume and the bank density, never from a swelled or shrunk figure.
For a battered (sloped-wall) dig, the entered dimensions are the floor of the excavation and the walls are cut back above it. A straight trench with constant cross-section is an exact prism — trapezoid cross-section area × length — while a four-sided pad or a circular pier is a frustum, handled with the exact frustum formula so the over-dig is never approximated.
Soil swell & shrinkage reference
Swell (bulking) and shrinkage vary with soil type, moisture, particle size and how the material is handled. The table below gives representative bank densities and typical swell and shrinkage ranges for common soils and rock, gathered from standard earthwork references.
Use them as starting points. Every value in the calculator is editable, so if you have a geotechnical report or a supplier's figure for your site, enter it and the results update immediately.
| Soil / rock type | Bank density (kg/m³) | Swell % (bank → loose) | Shrinkage % (bank → compacted) |
|---|---|---|---|
| Topsoil | 1,250 (1,200–1,600) | 30% (25–35%) | 12% (10–15%) |
| Sand | 1,600 (1,500–1,700) | 15% (10–20%) | 10% (5–15%) |
| Gravel | 1,750 (1,650–1,850) | 12% (10–20%) | 10% (5–15%) |
| Common earth / loam | 1,450 (1,350–1,600) | 25% (20–30%) | 15% (10–20%) |
| Clay (dry / firm) | 1,650 (1,550–1,750) | 33% (30–40%) | 20% (15–25%) |
| Wet / heavy clay | 1,900 (1,780–2,020) | 25% (20–30%) | 15% (10–20%) |
| Soft / rippable rock | 2,100 (2,000–2,300) | 40% (30–45%) | n/a |
| Blasted / broken rock | 2,400 (2,200–2,700) | 60% (50–70%) | n/a |
These are typical assumed ranges, not guaranteed constants — swell and shrinkage depend heavily on moisture, soil structure and handling. The calculator ships one default per soil type and lets you edit every factor. For anything load-bearing or contractual, confirm against a geotechnical report.
Frequently asked questions
How much does soil swell when you dig it?
Loosened soil bulks up by its swell factor: common earth by about 25%, sand and gravel by 10–20%, dry clay by 30–40%, and blasted rock by 50–70%. So a hole measuring 10 m³ in the ground yields roughly 12.5 m³ of loose common-earth spoil to haul away. The calculator applies this automatically — loose volume = bank volume × (1 + swell).
What is a swell factor and why does it matter?
Swell (or bulking) is the percentage a soil's volume increases when it is dug and loosened from its compact in-ground state. It matters because you order haulage against the loose volume, not the neat measured hole. Ignoring swell — or, worse, confusing it with shrinkage — under-books your skips or trucks and is the most common excavation-estimating error.
How many truckloads of dirt will I need to haul?
It depends on whether the load is limited by volume or by weight. The calculator computes both — loose volume ÷ truck volume capacity, and spoil weight ÷ truck payload — and takes whichever is larger, because a truck fills up on light bulky topsoil but hits its weight limit on wet clay or rock long before it is full. The rail labels which limit is binding.
What is the difference between bank, loose and compacted volume?
Bank is the in-situ soil as it sits undisturbed in the ground — the volume you measure. Loose is that same soil after digging, swelled up by the swell factor — the volume you haul. Compacted is the soil placed back as fill and rolled down, shrunk by the shrinkage factor — the volume it occupies in a finished embankment or backfill. Same material, same weight, three different volumes.
How do I calculate trench excavation volume?
For a plumb-walled trench it is length × width × depth, multiplied by the number of identical trenches. Choose the Trench shape, enter those dimensions and a count, and the calculator returns the bank volume plus the swelled loose volume and load count. If the walls are battered (sloped), add the batter ratio in the Advanced panel and the tool uses the exact trapezoid-sweep formula for the over-dig.
What is batter, and does the tool handle sloped trench walls?
Batter is the side slope of an excavation, quoted as a horizontal-to-vertical ratio (for example 1:1). Yes — enter a batter ratio in a zone's Advanced panel and the calculator over-digs the walls above the entered floor dimensions, using an exact prism formula for trenches and an exact frustum formula for pads and pier holes. The OSHA Type A/B/C presets are offered for reference only and are not a safety determination — consult a competent person or engineer for shoring and sloping decisions.
How does the backfill / borrow calculation work?
Enter the volume of the structure that will sit in the hole (a footing, a pipe, a tank) in the Advanced panel. The tool works out the compacted fill needed around it, converts that back to a bank-equivalent order via the shrinkage factor, and compares it to what you dug. If you dug more than you need back, the surplus is spoil to export (converted to loose for hauling); if you need more, the shortfall is borrow to import.
Can I use metric or imperial units?
Both. Toggle at the top of the page: metric gives metres, cubic metres and tonnes; imperial gives feet, cubic yards and short tons. Switching converts every dimension and setting in place, and the calculator remembers your choice in your browser.
Is the calculator private?
Yes. Every calculation runs locally in your browser — your dimensions, soil factors and costs are never sent to a server. Your project is saved only in your own browser's local storage so it is still there when you come back.