Builder AI Tools › Materials calculators
Excavation and muck-away calculator
Work out how much spoil comes out of a trench or reduced dig once it bulks up, how much it weighs, and how many skips or grab lorry loads it takes to get rid of it.
- Spoil to remove (bulked)
- –
- Volume dug (in the ground)
- –
- Weight
- –
- 8-yard skips (by volume)
- –
- Grab lorry loads (16 t)
- –
Skip firms often cap the weight of soil in a skip, so heavy clay may need smaller skips. Ask before you book.
Why spoil takes up more room than the hole
Ground in the earth is compacted. Once dug, it loosens and takes up more space: this is called bulking. A 1 m³ hole in clay can fill 1.3 to 1.4 m³ of skip. The calculator multiplies the dug ("bank") volume by a bulking factor for the ground type, then works out weight from the in-ground density.
| Ground | Bulking factor | Weight in the ground |
|---|---|---|
| Topsoil | about 1.25 | about 1.4 t/m³ |
| Clay | about 1.35 | about 1.9 t/m³ |
| Sand and gravel | about 1.15 | about 1.8 t/m³ |
| Chalk | about 1.45 | about 1.8 t/m³ |
| Mixed soil and rubble | about 1.3 | about 1.8 t/m³ |
These are typical values: wet ground weighs more, and every site is different. Treat the answer as a planning figure, not a weighbridge ticket.
Worked example: a 10 m footing trench
A trench 10 m long, 600 mm wide and 1 m deep in clay is 6 m³ in the ground. Bulked, that is about 8.1 m³ of spoil weighing around 11.4 tonnes. That fills two 8-yard skips by volume, but at over 5 tonnes per skip many hire firms will not take it in an 8-yard skip. A single grab lorry load is often the cheaper option for this much soil.
Skip or grab lorry?
- Skips suit small digs and mixed waste. An 8-yard builders' skip holds about 6.1 m³, but heavy waste like soil and hardcore is usually limited to smaller skips or a weight cap.
- Grab lorries take around 12 to 16 tonnes in one go and load from a pile on the drive or kerb, with no permit for the road if the lorry does not stay. They are usually better value above about 6 m³ of spoil.
- Re-use on site: clean topsoil and subsoil can often be spread or used for landscaping, saving disposal costs. Check it is not contaminated.
Safety: trenches deeper than about 1.2 m, or any trench in loose ground, need support or battering back. Check for buried services with a cable avoidance tool and utility plans before you dig.
Questions
What is the bulking factor of soil?
It is how much the soil expands once dug. Typical values are 1.15 for sand and gravel, 1.25 for topsoil, 1.35 for clay and up to 1.5 for chalk and rock.
How many tonnes of soil fit in a skip?
By volume an 8-yard skip holds about 6 m³, which in clay would be over 8 tonnes. Most hire firms cap heavy waste far lower, so ask about soil and hardcore limits.
How much soil does a grab lorry take?
A typical 8-wheel grab lorry carries about 12 to 16 tonnes, roughly 6 to 9 m³ of loose soil depending on the ground.
Results are estimates for planning and ordering. Check quantities with your supplier and product data sheets, and anything structural or regulated with a qualified professional. See our terms.