What comes out is bigger than what you dug
Ground in place has been compacted by everything that has sat on it since it was laid down. Dig it and it breaks into lumps with air between them, and it never goes back to the volume it came from.
So a 10 cubic metre hole in clay gives you 13.5 cubic metres of spoil. In broken rock it is 15. The skips got ordered for 10.
This is the single commonest reason a groundworks job runs over on disposal, and as far as we can find, no other muck away calculator mentions it at all. So both figures sit side by side here permanently, the hole and the pile, because showing only one of them hides the thing you came to find out.
Typical bulking
- Sand: +12%. Barely bulks, which is why sand always looks like less spoil than it was.
- Gravel: +15%
- Topsoil: +25%
- Made ground: +30%
- Clay and chalk: +35%
- Broken rock: +50%, because broken rock is mostly gaps.
All of them move with how wet it is, more than with anything else.
Weigh the hole, not the pile
A mistake worth naming because it goes the other way and it is just as common.
Bulking adds air, not material. A cubic metre of clay weighs the same whether it is in the ground or sitting on a lorry: there is simply more of it to look at. So the weight comes off the in-situ volume at the in-situ density.
Multiply the bulked volume by the in-situ density and you over-estimate the weight by a third, and order a lorry you did not need.
Which limit decides the bill
Everybody says a muck lorry fills on weight. Work it through and for most excavated spoil it is volume, and the reason is bulking again: loose density is always lower than in-situ density. Clay at 1.9 tonnes a cubic metre in the ground is about 1.4 loose in a body, and 11 cubic metres of that is 15 tonnes against a 16 tonne payload. The body runs out first.
Weight does bite, on the genuinely dense stuff and on anything saturated: rock, wet clay, rubble with concrete in it. And hauliers spec bodies to match payload for typical muck, so the two limits sit close together and a wet week can flip which one decides the bill.
So the tool names the binding limit rather than just printing a number. "Five loads" tells you nothing. "Five loads, and weight runs out with three cubic metres of body going back empty every trip" tells you why a quote by body size was wrong.
Grab or tipper
A grab lorry loads itself, so there is no digger standing waiting and no muck-shifter on the payroll. The catch is reach: the spoil has to be within about seven metres of somewhere the lorry can legally stand, which on a terraced street decides it entirely.
A tipper is cheaper per tonne and always will be, but something has to load it and it needs room to get the body up. On a job with a machine already on site and space to work, it wins.
Whether the material is contaminated
Whether the material is contaminated. Made ground in particular can carry a disposal cost that has nothing to do with volume or weight, and finding that out after the first load has gone is expensive. If the site has industrial history, that is a question for a testing lab before it is a question for a haulier.
Bulking factors and densities here are typical published ranges. The haulier's own figures are the ones that end up on the invoice.
Next to it: skip sizes, which has a different problem entirely: the lorry can only lift so much, and aggregate for what goes back in, which compacts in the opposite direction to this.
Common questions
Why is there more spoil than the hole I dug?
Because ground in place has been compacted by everything that has sat on it since it was laid down. Dig it and it breaks into lumps with air between them, and it never goes back. Clay bulks by about a third, broken rock by half, sand by only about a tenth. A 10 cubic metre hole in clay gives you 13.5 cubic metres to cart away.
What is the bulking factor for clay?
Around 1.35, so a third more volume than the hole. Chalk is similar. Made ground is about 1.3, topsoil 1.25, gravel 1.15, sand only 1.12, and broken rock 1.5 because it is mostly gaps. Wet weather changes all of them.
How many grab lorry loads will I need?
It depends on which limit bites first, body size or payload, and the tool works out both and tells you which. An 8 wheel grab is around 11 cubic metres and 16 tonnes; a tipper is 12 cubic metres and 20 tonnes. Those figures vary by operator and the haulier’s own are the ones on the invoice.
Do muck away lorries fill on weight or volume?
The received wisdom says weight. Work it through and for most excavated spoil it is volume, because bulking adds air: loose density is always lower than in-situ density. Clay at 1.9 in the ground is about 1.4 loose in a body. Weight does bite on rock, wet clay and rubble with concrete in it, and the tool names which one is deciding rather than making you assume.
Should I weigh the spoil off the hole volume or the pile volume?
The hole. Bulking adds air, not material: a cubic metre of clay weighs the same whether it is in the ground or on a lorry, there is just more of it to look at. Multiplying the bulked volume by the in-situ density is a common mistake and it over-estimates the weight by a third.
Is this the same as a skip calculation?
Related but not the same. Skips have a separate problem: the lorry can only lift so much, so a big skip full of soil cannot be collected at all. There is a companion tool for that.