United Kingdom · Materials & DIY
Muck Away Calculator
Change the bulk density used
Enter the excavation dimensions. The calculator applies a bulking factor, because dug material takes up far more space than the hole it came out of, and returns tonnes and grab loads.
How much spoil does an excavation produce?
Multiply the excavation volume by a bulking factor of around 1.25 to 1.4, because material expands when dug, then by roughly 1.6 to 1.9 tonnes per cubic metre depending on the soil. A 10 cubic metre excavation typically produces 12.5 cubic metres of spoil weighing about 22 tonnes — around three grab loads.
How to use this calculator
- Measure the hole, not the finished elementAn excavation is always larger than what goes into it — working space around a foundation, batter on the sides of a deep dig, and over-dig at the base all add volume.
- Leave the bulking allowance at 30%This field is not a waste margin here. It is the bulking factor: material that occupied one cubic metre in the ground occupies noticeably more once it is dug and loose.
- Set the density for the soilClay is heavier than sand, and both are heavier wet. This is the input that decides how many lorry movements you pay for.
- Read grab loads, not just tonnesMuck away is priced and delivered in loads. Knowing you need three rather than two changes the programme as well as the cost.
How the calculation works
Two multiplications, and the first is the one that catches people out.
Soil in the ground is compacted by everything above it and by time. Dig it and you break that structure, introducing air between the particles. The material expands — typically by 20 to 40 per cent depending on the soil — and that expanded volume is what has to go into a lorry.
Clay bulks the most, often by 30 to 40 per cent, because it comes out in cohesive lumps with substantial voids between them. Sand and gravel bulk least, around 10 to 20 per cent, because the particles rearrange more efficiently. Rock, once broken, can bulk by 50 per cent or more.
Density then converts loose volume into weight. Muck away is generally priced by the load rather than the tonne, but weight determines whether a lorry is full before it is loaded to capacity — with wet clay, a grab lorry frequently reaches its weight limit while there is visible space left in the body.
loose volume = dug volume × bulking factor; tonnes = loose volume × densityBulking factors by material
| Material | Bulking factor | Density in place (t/m³) |
|---|---|---|
| Sand and gravel | 1.10 – 1.20 | 1.7 – 1.9 |
| Topsoil | 1.20 – 1.30 | 1.3 – 1.5 |
| Mixed subsoil | 1.25 – 1.35 | 1.7 – 1.9 |
| Clay | 1.30 – 1.40 | 1.8 – 2.1 |
| Wet clay | 1.30 – 1.40 | 2.0 – 2.2 |
| Broken rock | 1.50 – 1.60 | 2.2 – 2.6 |
| Made ground, mixed rubble | 1.30 – 1.50 | 1.6 – 2.0 |
Worked example: strip foundations
A strip foundation trench 6 m by 3 m in plan, dug 600 mm deep, is 10.8 cubic metres in the ground.
At a 30 per cent bulking factor that becomes 14.04 cubic metres of loose spoil. At 1.8 tonnes per cubic metre that is 25.3 tonnes.
An 8-wheel grab lorry typically takes around 12 to 14 tonnes, so that is two loads with a little left over — which in practice means three, because nobody schedules a third lorry for two tonnes. This is exactly the situation where knowing the number in advance lets you either reduce the dig or accept the cost with your eyes open.
If the same trench were in wet clay at 2.1 tonnes per cubic metre and a 35 per cent bulking factor, the figure rises to 30.6 tonnes — the same hole, nearly a full extra load.
What determines the cost, and it is rarely the volume
Disposal cost is driven by what the material is, not how much of it there is. Clean, uncontaminated subsoil going to an inert landfill or a reuse site is the cheapest outcome. The same volume classified as contaminated can cost several times more, and needs testing, documentation and a licensed facility.
Made ground is the common surprise on domestic sites in older urban areas. Anything that has been built on before may contain demolition rubble, ash, clinker or worse, and what looked like a straightforward dig becomes a waste classification problem.
Access is the other cost driver. A grab lorry needs to get within reach of the pile, and where it cannot, the material has to be double-handled into a skip or barrowed out. That can easily cost more than the disposal itself.
There is also a legal dimension. Excavated material leaving a site is controlled waste, and moving it requires a registered carrier and a waste transfer note. Tipping spoil on a neighbouring field as a favour is fly-tipping, and the liability sits with the producer as well as the carrier.
Reusing spoil on site avoids the whole problem where the ground conditions allow it. Subsoil can often be used to level or landscape elsewhere on the plot, and topsoil is genuinely valuable — stripping it separately and stockpiling it is worth the extra handling.
Assumptions and limitations
- Bulking factors are typical ranges — the actual figure depends on the specific soil and how it is dug
- Assumes a uniform excavation depth; battered sides and over-dig add volume the calculator cannot see
- Density defaults to mixed subsoil and rises considerably for wet clay
- Grab load capacity assumes a standard 8-wheel lorry and varies by operator and weight limit
- Takes no account of waste classification, which drives cost far more than volume
- Does not address duty of care, waste transfer documentation or carrier registration
Questions people ask about this in United Kingdom
How much does soil bulk up when excavated?
Typically 20 to 40 per cent by volume. Sand and gravel bulk least at around 10 to 20 per cent; clay bulks most at 30 to 40 per cent; broken rock can exceed 50 per cent.
That expansion is why a 10 cubic metre hole produces noticeably more than 10 cubic metres of material to remove.
How many tonnes in a grab lorry?
An 8-wheel grab lorry typically carries 12 to 14 tonnes, though the limit is set by weight rather than volume. With wet clay the lorry often reaches its weight limit while there is visible space left in the body.
How much does muck away cost?
It depends far more on what the material is than how much there is. Clean inert subsoil going to a reuse site is cheapest; material classified as contaminated needs testing, documentation and a licensed facility, and can cost several times more per load.
Can I dump excavated soil on my own land?
Sometimes, and reusing it on the same site is usually the cheapest and simplest option where levels allow. Moving it off site makes it controlled waste, requiring a registered carrier and a waste transfer note — and tipping it elsewhere without those is fly-tipping.
Is topsoil worth keeping separate?
Yes. Topsoil has real value for landscaping and is expensive to buy back in. Stripping it separately and stockpiling it costs a little extra handling and frequently saves more than it costs, particularly on a plot that will need soil for beds or lawn later.
What is made ground and why does it matter?
Ground that has been previously built on or filled, often containing demolition rubble, ash or clinker. It bulks unpredictably, weighs differently from natural soil, and may need testing before disposal. On urban plots it is the most common reason a dig costs more than estimated.
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Method, source and review date
- How it is worked out
- Excavated volume with a bulking allowance, converted to weight and grab loads
- Formula used
tonnes = excavation volume × bulking factor × soil density- Basis
- Typical supplier bulk densities, editable on the page
- Last reviewed
- Confidence
- Medium
Bulking factors vary widely with soil type — clay bulks far more than sand — and density varies with moisture. Contaminated or made-up ground changes both the cost and the disposal route entirely.
Spotted a figure that has moved, or a formula you can show is wrong? Tell us — send a correction. Fixes to rates and formulas are treated as urgent.
Disclaimer
Quantities are an estimate for planning and ordering. Site conditions, wastage, cuts and delivery minimums all change what you actually need — always confirm with your supplier or the person laying the material before ordering.