Loose versus compacted: why there are two numbers
Crushed rock is sold by the tonne but placed by the cubic metre, so the weight of a cubic metre matters at both ends of the job. The catch is that the same rock weighs different amounts depending on whether it is sitting loose in a stockpile or rolled tight in a pavement.
Loose is how it arrives: tipped off the truck with air gaps between the stones. Compacted is after it has been spread in a layer, watered and rolled, which squeezes the air out and packs the particles together. Compacting a well graded crushed rock lifts its density by roughly a third, which is why a cubic metre of loose rock does not fill a cubic metre of finished pavement.
Weight by product (tonnes per cubic metre)
| Product | Loose (t/m³) | Compacted (t/m³) |
|---|---|---|
| Crushed rock / road base (20mm) | 1.5 – 1.6 | 2.0 – 2.2 |
| Crushed rock (40mm) | 1.5 – 1.6 | 2.0 – 2.2 |
| Crusher dust (5mm minus) | 1.6 – 1.8 | 1.9 – 2.1 |
| Single-sized aggregate (10–20mm) | 1.4 – 1.5 | n/a (does not compact) |
| Scoria (lightweight) | 0.8 – 1.0 | 1.0 – 1.2 |
| Sand | 1.4 – 1.6 | 1.6 – 1.8 |
| Topsoil | 0.9 – 1.4 | 1.1 – 1.5 |
Figures are indicative and vary with source rock, grading and moisture. For an exact figure on the product you are ordering, ask us and we will give you the current bulk density.
The trailer-load reality
This is where weight catches people out. A cubic metre of crushed rock is over a tonne and a half, but the trailers people bring to collect it are rated for far less.
Turning volume into tonnes for your order
If you know the volume you need, multiply by the density to get the tonnes to order. Use the compacted figure for anything that gets rolled, and add about 10 percent for compaction and waste.
For example, a driveway base of 50 m² at 150mm compacted depth is 7.5 m³. At roughly 2.1 t/m³ compacted that is about 16 tonnes, so you would order around 17 to 18 tonnes to cover compaction. Our how much road base do I need guide walks through the full method.