Excavation Calculator
A 10 m³ hole makes 13.5 m³ of clay.
A 10 m³ hole makes 13.5 m³ of clay. Excavation volume, the larger bulked volume that has to be carted away, weight and disposal cost.
Spoil to remove
13.5 m³
From a 10 m³ hole — Clay bulks by 35%
Ground expands when it is dug. Clay bulks by about 35% and broken rock by half, because excavation destroys the packed structure and leaves voids that never fully close again. A 10 m³ hole therefore produces 13.5 m³ of clay spoil, and skips are hired against the bulked figure. The weight figure is the one that decides plant and haulage. Clay at 1.9 tonnes a cubic metre means that same 10 m³ hole yields 19 tonnes — three lorry loads by weight even if the volume would fit in two. Backfilling reverses part of the problem but never all of it: compacted backfill occupies less than the loose spoil it came from, so there is almost always surplus to remove even on a job that fills its own hole back in.
How the Excavation Calculator works
Excavation volume, the larger bulked volume that has to be carted away, weight and disposal cost. Ground expands when it is dug, and skips are hired against the bulked figure rather than the hole.
Also known as: how many skips for a dig · soil bulking factor · how much spoil from a trench · weight of excavated clay
Where to go next
The Excavation question rarely arrives on its own. These are the ones that usually come with it:
- Mortar Calculator — Dry volume is a third more than wet. That is the whole thing.
- Rebar Calculator — Counts the bars. Does not design the slab.
- Pipe Volume Calculator — Watch the velocity, not just the volume.
- Speed Distance Time Calculator — Any one of the three from the other two, in four units.
Sources
Frequently asked questions
What is soil bulking?
The expansion that happens when ground is excavated. Digging destroys the packed structure and leaves voids, so clay bulks by about 35%, sand by 12% and broken rock by half.
How many skips will I need?
Work from the bulked volume, not the hole. A 10 m³ clay excavation produces 13.5 m³ of spoil, which is two 8 m³ skips rather than the one and a bit the hole suggests.
How much does excavated soil weigh?
Clay is around 1.9 tonnes per cubic metre, sand 1.6 and broken rock 2.4. Weight often decides haulage before volume does — 10 m³ of clay is 19 tonnes.
Does backfilling reduce the spoil?
Partly. Compacted backfill occupies less than the loose spoil it came from, so there is almost always surplus to remove even on a job that fills its own hole back in.
Do I need to allow for working space?
For anything you have to get into, yes. Trenches and foundations are usually dug wider than the finished element to allow for formwork and access, which adds to both the dig and the spoil.
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Related calculators
Mortar Calculator
Dry volume is a third more than wet. That is the whole thing.
OpenRebar Calculator
Counts the bars. Does not design the slab.
OpenPipe Volume Calculator
Watch the velocity, not just the volume.
OpenSpeed Distance Time Calculator
Any one of the three from the other two, in four units.
Open