Foundation Excavation Calculator

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.

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.

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.