Foundation Excavation Calculator

Calculate foundation dig volume for slab, crawlspace, or basement with working room allowance and optional strip footings.

Part of the Excavation & Earthworks calculators — see all tools in this category.

Foundation Type

Shallow excavation for slab-on-grade construction (typical depth: 150mm / 6in)

Dimensions

Pre-filled from foundation type; adjust as needed

Extra space added to all four sides for access and formwork

Soil Type
Strip Footings (Optional)
Truck Estimation (Optional)

Results

Excavation Area (with working room)

13.20 m × 11.20 m

Foundation + 0.60 m working room per side

Total Bank Volume
22.18m³

In-situ volume to excavate

Total Loose Volume
29.94m³

For hauling and disposal

Total Weight
42142kg

In-ground weight

How It Works

This calculator helps you estimate the volume of earth to excavate for a building foundation. It supports three common foundation types and accounts for working room — the extra space you need beyond the foundation footprint for access, formwork, and waterproofing. For a full takeoff workflow before you lock the dig dimensions, review the excavation planning guide and compare the overall pit against the broader excavation calculator.

Foundation Types

  • Slab: Shallow excavation (typically 150mm / 6″) for slab-on-grade construction. The most common residential foundation type in warm climates.
  • Crawlspace: Medium excavation (typically 600mm / 2′) providing access space under the structure for utilities and maintenance.
  • Basement: Deep excavation (typically 2.4m / 8′) for a full below-grade living or storage space.

Working Room

Working room is added to all four sides of the foundation. The excavation dimensions are:

  • Dig Length = Foundation Length + (2 × Working Room)
  • Dig Width = Foundation Width + (2 × Working Room)

A standard working room of 600mm (2 ft) per side adds 1.2m (4 ft) to each dimension. Deep basements or complex waterproofing may require more working room. If you need to show that added width in the estimating math, the excavation formulas guide walks through the dimension-to-volume steps.

Strip Footings

Strip footings are trenches below the main excavation that carry structural loads. Their volume is calculated separately as: Footing Length × Footing Width × Footing Depth. The total volume is added to the main excavation volume for hauling estimates.

When those footing trenches change how much spoil you have to stage beside the house pad, run the loose material through spoil pile planning so the foundation dig estimate carries through to haul-off and setback decisions.

Frequently Asked Questions

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Foundation Excavation Calculator | ConstructCalculators