Foundation excavation = each footing size plus working space on every side, × depth, added up for all pads and strips. Eight 1.5 × 1.5 m pads and 40 m of 0.6 m strip footing, dug 1.2 m deep with 300 mm working space, is 42.3 + 57.6 = 99.9 m³, about 13 loads of spoil.
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Foundation Excavation Calculator
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Results
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Foundation excavation (bank)
99.94m³
Pads (8)
42.34 m³
Strip footings
57.60 m³
Loose volume to haul
124.92 m³
Truck loads
13 loads
Where pads and strips meet, the overlap is counted twice: deduct it if it is large.
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Generated with myconstructioncalculator.com. Estimates for planning and ordering only; verify against drawings and specifications.
Formulas
Pad dig = (L + 2s) × (W + 2s) × D × n (prismoidal if sides slope)Strip dig = length × (b + 2s) × D (trapezoid section if sides slope)Total = pads + strips
s = working space each side, D = depth to the bottom of blinding.
Worked example
Eight pads 1.5 × 1.5 m and 40 m of strip footing 0.6 m wide, 1.2 m deep, 300 mm working space, vertical sides:
Pads = 2.1 × 2.1 × 1.2 × 8 = 42.34 m³
Strips = 40 × 1.2 × 1.2 = 57.60 m³
Total = 99.94 m³ → loose 124.9 m³ → 13 loads at 10 m³
Assumptions
All pads the same size; for mixed sizes, run the calculator per size and add.
Depth is from existing ground; any reduced-level dig over the whole site is extra: see bulk excavation.
Frequently Asked Questions
How do I calculate excavation for foundations?
Add the working space to each side of every footing, multiply by the depth to the bottom of the blinding, and add up all the footings. Strip footings are length × (width + 2 × working space) × depth.
How much working space is needed around footings?
Typically 300–600 mm each side for formwork and access. Earth-formed footings cast directly against the soil need none.
Do I count the overlap where pads and strips meet?
The calculator adds them separately, so a small overlap is counted twice. Deduct it if your layout has many large junctions.
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