The volume of material you need to move is not the volume you dug, because soil swells when it is excavated. A cubic metre of undisturbed clay becomes about 1.25 cubic metres of loose spoil in a trailer, and more if it is wet or rocky — which means a job that looks like six trailer loads is eight, and the eighth is the one that has to be fitted in after the hire company closes. This takes the area and depth, applies the bulking factor, and turns the result into trailer loads, barrow loads and tonnes.
Ground, bulking and transport
Excavated ground swells. A cubic metre in the ground is more than that in a trailer.
150 mm for a patio dig; 300 mm or more for a foundation trench.
Sand and gravel 10%, clay 25 to 40%, rock 50% or more.
A typical single-axle tipping trailer holds about 1.5 m³ heaped.
A builder’s barrow is about 80 litres; a small one 65.
Hire, skip, or a tip run — whatever one load actually costs you.
Result
Bulking: the same soil, more volume
Soil in the ground is compacted by its own weight and by everything that has happened to it. Excavate it and that structure is destroyed: the material breaks into lumps with air between them, and the same mass now occupies more space. The increase is called bulking, and it is between ten and sixty percent depending on the material.
Sand and gravel bulk least, around ten to fifteen percent, because the particles are already rounded and do not hold much air. Clay bulks twenty-five to forty percent. Rock bulks fifty percent or more, because broken stone is mostly void. And wet material bulks more than dry, because the water stops the fines settling into the gaps.
The last load is the expensive one
Loads are whole, so the remainder always rounds up — and the final load is always part-empty. Nine cubic metres in the ground becomes 11.25 loose, which at 1.5 cubic metres a load is eight loads, and the eighth is three-quarters empty. You pay for the whole load either way, whether that is trailer hire by the day, a tip fee by the load, or a skip by the size.
This is why the decision between a skip and a trailer is usually about the number of loads rather than the total volume. Below about four loads, a trailer and a tip run is cheaper and quicker. Above about six, a skip becomes worth it even though you are paying for capacity you will not fill, because it removes the trips entirely.
A trailer fills to its volume limit long before its weight limit with topsoil, but the reverse is true with sand, gravel and anything wet — and those are exactly the materials that get loaded last.
Check the plated gross weight of the trailer and the towing capacity of the vehicle. Eleven cubic metres of spoil is eighteen tonnes, which is not a car trailer's job.
What the barrow count really means
A hundred and forty-one barrow loads is the number that decides whether a job is doable by hand. At roughly a minute and a half per round trip — fill, push, tip, return — that is three and a half hours of barrowing, and it is three and a half hours on top of the digging, not instead of it.
It also scales badly with distance. The round trip is mostly walking, so doubling the distance from the hole to the pile roughly doubles the time without changing the volume at all. Where the material has to go through a house, up a slope or across soft ground, the honest answer is usually to move the pile closer, or to accept a much longer day.
| Method | Per load | Loads for 11 m³ | Total time | Note |
|---|---|---|---|---|
| Car trailer and tip | 1 trip | 8 | 1 to 2 days | Needs a tow bar and a licence |
| Builder's barrow | 80 L | 141 | 3.5 hours | Plus the digging |
| Skip, 8 yd³ | 6 m³ | 2 | Delivered | Needs a permit if on the road |
| Grab lorry | 10 m³ | 2 | One visit | Can lift over a wall or hedge |
| Bulk bag | 0.9 m³ | 13 | Collected | Must be liftable by crane |
| Wheelie bins | 0.24 m³ | 47 | By collection | Only for clean spoil |
A worked example
- In the groundSixty square metres at 150 mm is 9.0 m³ — a modest patio dig.
- After bulkingAt twenty-five percent that becomes 11.25 m³ loose.
- Trailer loadsAt 1.5 m³ a load, that is 8 loads, and the last one is only three-quarters full.
- Barrow loadsAt 80 litres, 141 barrow loads, which is about 3.5 hours of barrowing.
- WeightAt 1.6 tonnes per cubic metre, about 18 tonnes — well beyond a small trailer's plated capacity.
Eighteen tonnes is the number to stop at. It is two grab lorry visits, or a very long weekend, and it is the reason a job that looked like a few trailer loads turns into the hardest part of the project.
Where it goes
Spoil has to go somewhere legal. Clean soil and hardcore can often be reused on site as fill or as a base, which is free and avoids the whole question; mixed or contaminated material cannot, and a waste transfer station will charge by weight and may reject it. Asbestos, treated timber and anything with Japanese knotweed in it are a specialist disposal, not a tip run.
Reusing on site is usually the best answer for the first few cubic metres. Raised beds, a bank, a levelled area, or the bottom layer of a new bed — the raised bed figure and the mulch figure both describe places where clean subsoil is an asset rather than a problem. Where the material is green waste instead of spoil, the pruning waste figure sizes it, and the compost bin figure tells you how much of it can stay.
Do
- Apply a bulking factor — the loose volume is not the hole volume.
- Check the trailer's plated weight as well as its volume.
- Compare a skip and a grab lorry against the number of trips.
- Reuse clean spoil on site before paying to remove it.
- Put the pile as close to the hole as you can.
Avoid
- Ordering a trailer by the hole volume and running out of capacity.
- Loading sand or gravel to the volume limit and exceeding the weight limit.
- Underestimating the barrowing, which is usually the slowest part.
- Assuming everything can go to a tip as clean spoil.
- Piling spoil where it has to be moved twice.
Where the numbers stop being true
The bulking factor is a single percentage for the whole job and real jobs have mixed material: topsoil over clay over rubble, each bulking differently. If the dig crosses distinct layers, it is worth applying a different factor to each, or using the highest and accepting the estimate is generous.
Nothing here accounts for what happens to the material in the trailer. It compacts on the way, so a load that was heaped at the hole settles on the road, and you can sometimes fit slightly more than the nominal capacity. Equally, material left in a heap overnight absorbs water and gets heavier without getting bigger.
The barrowing time is a rough rate of a minute and a half per round trip, which is realistic on the flat over a short distance and wildly optimistic over soft ground, uphill, or through a house. Treat it as a lower bound.
How the figures are produced
Area times depth gives the volume in the ground. The bulking percentage is applied to give the loose volume, which is what has to be moved. Trailer loads are the loose volume divided by trailer capacity, rounded up, and barrow loads use the barrow capacity the same way. Weight uses 1.6 tonnes per cubic metre of loose spoil, and the barrowing hours are a minute and a half per round trip.
Questions people ask
Why is it more than the hole?
Bulking. Excavated soil has air in it that it did not have in the ground, so the same material occupies more space — typically 25% more for clay.
How much does a trailer hold?
About 1.5 cubic metres heaped for a typical single-axle tipping trailer. Check the plated weight too, because spoil is heavy.
Skip or trailer?
Below about four loads, a trailer and a tip run. Above about six, a skip, because it removes the trips.
How heavy is it?
About 1.6 tonnes per cubic metre loose, so eleven cubic metres is around eighteen tonnes.
Can I put it in a skip?
Clean soil and hardcore, yes. Mixed waste, treated timber and anything contaminated need a licensed transfer station, and some things need a specialist.
How long does it take by barrow?
About a minute and a half per round trip on the flat. A hundred and forty-one loads is three and a half hours, plus the digging.