Excavation Calculator
Estimate how much soil a rectangular dig will produce. Enter the pit or trench length, width, and dig depth in metres, plus an allowance percentage (preset to 5%), and the page returns the bank volume in cubic metres so you can plan skips, trucks, and backfill.
Your result will appear here.
Excavation Calculator online
Estimate how much soil an excavation contains from its length, width and depth, with an allowance for over-dig — and a clear line between the volume in the ground and the bigger volume on the truck.
How it works
The calculation is Excavation volume = L × W × D × (1 + Allowance ÷ 100). Length and width are the plan dimensions of the dig and D is the vertical depth, all in metres. The allowance field defaults to 5% for over-dig and uneven trench walls; it is not a bulking factor, so if your soil swells heavily on loosening, raise the allowance or handle swell in a separate step.
Worked example
A foundation pit 8 m long, 3 m wide, and 1.5 m deep with the default 5% allowance: bank volume = 8 × 3 × 1.5 = 36 m³; planned volume = 36 × 1.05 = 37.8 m³. In cubic yards that is 37.8 × 1.308 ≈ 49.4 yd³. At roughly 8 m³ of loose soil per tipper, expect about five loads before compaction and swell are considered.
Units
Output is in cubic metres: 1 m³ = 35.3147 ft³ = 1.308 yd³. A handy site conversion is 1 m of depth over 1 m² of plan area = 1 m³. If your dimensions are in feet, convert first (1 ft = 0.3048 m) rather than converting the answer afterwards, because volume scales with the cube of any linear error.
Practical tips
- Batter or step trench walls in the dimensions you enter. A 1 m wide trench that caves to 1.3 m at the top holds about 15% more than the neat L × W × D figure.
- Keep bank cubic metres (in the ground) separate from loose cubic metres (in the truck). Clay and dense soil can swell 25–35% on excavation, so a 37.8 m³ dig may need haulage for around 47–51 m³ loose.
- Measure depth from the stripped surface, not from the top of the grass, and re-check after the first pass of the machine.
- Use the figure for plant and haulage planning only. Shoring, batter angles, groundwater, services, and permits need site-specific assessment by a competent contractor or engineer.
Edge cases and limitations
- Battered sides multiply volume. The rectangle here assumes vertical sides. A trench dug with 1:1 batters for safety has a trapezoidal section: a 1 m wide, 1.5 m deep trench widens to 4 m at the top, and its cross-section is (1 + 4) ÷ 2 × 1.5 = 3.75 m² — two and a half times the 1.5 m² of the vertical cut. Price the trapezoid, not the slot.
- Bulking is real and separate. Soil swells when dug: sand and gravel by roughly 10–15%, topsoil 20–25%, clay 30–40%, blasted rock 50% or more. The allowance field is for over-dig, not swell — apply bulking afterwards to get truck volumes.
- Backfill needs more than the hole. Compacted fill occupies less volume than the bank it came from (clay can shrink about 10% on compaction), so a dig-and-backfill job can still need imported material. Bank, loose and compacted are three different volumes for the same soil.
- Water is a volume too. Below the water table, plan for pumping and for saturated soil behaving differently — weights per load rise and tipper counts based on dry density understate the haulage.
Privacy and browser processing
The calculation runs entirely in your browser — the dimensions you enter are never uploaded.
Frequently asked questions
What allowance should I enter for a hand-dug trench?
Start at 10% rather than the preset 5%, because hand trimming leaves wavy walls and a lumpy base. For a trench 10 × 0.6 × 1.2 m the neat volume is 7.2 m³; at 5% the tool gives 7.56 m³, while at 10% it gives 7.2 × 1.10 = 7.92 m³.
Does the result include soil bulking?
No, the tool returns the in-ground volume plus your allowance only. To cover bulking, add the swell to the allowance: for soil that swells 25%, a 20 m³ dig becomes roughly 25 m³ loose. Set the allowance field to about 30% to get 20 × 1.30 = 26 m³ for truck planning.
How many skip loads is 37.8 m³ of soil?
Divide by the container’s loose capacity and round up. Large builders’ skips hold about 7–8 m³ loose, so 37.8 m³ needs at least five skips before swell; with 25% bulking (about 47 m³ loose) it becomes six to seven skips.
Can I use this for a circular soakaway or manhole?
Not directly — this page assumes a rectangular plan. For a circular pit, compute its plan area as π × r² first. A 2 m diameter, 1.5 m deep soakaway is 3.1416 × 1 × 1.5 ≈ 4.71 m³ before any allowance.