Foundation and Sitework Estimates: Footings, Excavation, and Paving
How to estimate concrete footings, excavation volume, retaining wall concrete, and asphalt driveway tonnage before groundwork begins.
Sitework and foundation estimates are almost entirely volume calculations — get the dig or pour dimensions right, and the material quantity follows directly.
Concrete footings: length, width, and depth to cubic yards
Footing volume is length × width × depth, converted from cubic feet to cubic yards by dividing by 27 (since there are 27 cubic feet in a cubic yard). This is the foundation calculation everything else in a build depends on getting right.
Excavation volume: the dig before the pour
A 20 ft × 10 ft × 4 ft deep excavation works out to 800 cubic feet, or 800 / 27 ≈ 29.63 cubic yards — the standard unit used for billing and hauling. Excavated soil also expands (bulks) 15-30% once dug up, which matters if you're calculating how much loose material needs hauling away.
Retaining wall concrete: same volume logic, applied to a wall
A 30 ft long, 3 ft high, 1 ft thick wall requires 30 × 3 × 1 = 90 cubic feet, or 90 / 27 ≈ 3.33 cubic yards of concrete — again, length × height × thickness, then divided by 27.
Asphalt driveway: volume converted to weight, not just volume
Asphalt is priced by the ton, not the cubic yard. A 600 sq ft driveway paved 3 inches (0.25 ft) thick has a volume of 150 cubic feet; multiplying by asphalt's typical density (145 lb/cu ft) and dividing by 2,000 lb/ton gives roughly 10.88 tons needed.
Sequencing a sitework estimate
Excavation comes first, footings and walls next, and paving last — but all four numbers are useful to have before a contractor bid arrives, so you can sanity-check the quote. Run your project through the footing calculator, excavation volume calculator, retaining wall concrete calculator, and asphalt driveway calculator.