Excavation Volume Calculator NZ 2026

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.

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%
9.4 m³
loose volume to cart away
In-ground volume7.5 m³
Approx weight~13 t
Truckloads2

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

How it works

The in-ground bank volume is length times width times depth. The loose volume adds the swell percentage, because soil bulks up when it is dug. The approximate weight uses a loose density of about 1.4 tonnes per cubic metre. Truckloads are the loose volume divided by the truck capacity, rounded up.

Worked example

A 5 by 3 metre hole dug to 0.5 metres deep is 7.5 cubic metres in the ground. With 25 percent swell for common soil, that becomes about 9.4 cubic metres loose, weighing roughly 13 tonnes. At 6 cubic metres a truck, that is 2 truckloads to cart away. Heavy clay at 40 percent swell would push the loose volume to about 10.5 cubic metres.

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Frequently asked questions

What is soil swell or bulking?

When soil is dug it breaks up and takes up more space than it did in the ground. This bulking, or swell, is typically 10 to 15 percent for sand, around 25 percent for common soil, and 40 percent or more for clay and rock. It increases the volume you cart away.

How many truckloads will my excavation be?

Divide the loose volume, after swell, by the truck capacity and round up. A 6 cubic metre tip truck carts away about 6 cubic metres of loose material per trip. This calculator estimates the loads so you can budget cartage and disposal.

How do I estimate disposal weight?

Loose excavated soil weighs roughly 1.4 tonnes per cubic metre, though wet or clay soils are heavier. Transfer stations and cleanfills often charge by weight, so the tonnes estimate here helps you budget disposal, but confirm rates with your site.