Excavation Volume Calculator

This calculator works out how much material you will dig out of an excavation, how much it becomes once it is loosened, and roughly how many truckloads it takes to cart away, which is essential for pricing any digging job in New Zealand. Excavation is needed for foundations, retaining walls, pools, drainage, water tanks and levelling a section, and it catches people out for one key reason: soil swells when it is dug. A neat hole measured in the ground might be a certain number of cubic metres, but once that soil is broken up it bulks up by anywhere from 10 to 40 percent, so the volume you actually load onto trucks, and pay to dispose of, is larger than the hole. This bulking, or swell, varies with the material, from around 10 to 15 percent for sand up to 40 percent or more for clay and rock. You enter the length, width and average depth of the excavation, and a swell percentage for your soil type, and the calculator returns the in-ground bank volume, the loose volume after swell, an approximate weight in tonnes, and the number of truckloads at a typical truck capacity. This helps you brief a contractor, sense-check a quote that is priced per cubic metre or per load, and budget for disposal, which is often charged by weight or volume at a transfer station or cleanfill. For sloping or irregular sites, break the dig into sections and add them up. Treat the figures as an estimate; real swell, density and truck sizes vary, and a contractor's site assessment will be more precise.

Swell varies by soil: ~15% sand, ~25% common soil, 40%+ clay or rock. Weight uses ~1.4 t/m³ loose. An estimate only.