The conversion
area covered (m²) = cubic metres ÷ depth (m)
- 2 tonnes of brickies sand is 2 ÷ 1.5 = 1.33 m³, enough to bed pavers 30 mm deep over 44 m².
- 5 m³ of bark mulch weighs only 5 × 0.35 = 1.75 t, and covers 67 m² at 75 mm.
- 10 tonnes of road base is 10 ÷ 2.2 = 4.5 m³ once compacted. That is the figure for a base: the paver calculator orders road base by its compacted density, so the tonnes cover the finished layer.
Bulk densities compared
Bulk density is the weight of a cubic metre of loose material, air gaps included. It varies with the stone, the grading and above all with moisture. The table compares the figures used on GardenMaths with the indicative figures published by Australian Native Landscapes (ANL), a large Sydney landscape supplier:
| Material | GardenMaths (t/m³) | ANL (t/m³) |
|---|---|---|
| Garden soil / topsoil | 1.3 | garden mix 1.2, topsoil 1.4 |
| Sandy loam / top dressing | 1.4 | organic top dressing 1.4 |
| Sand | 1.5 | brickies 1.45, river 1.5, fill 1.4, Sydney sand 1.3 |
| 20 mm gravel / blue metal | 1.5 | blue metal 1.45, other gravels 1.5 |
| River pebbles | 1.55 | river gravel 1.55 |
| Crusher dust | 1.6 | dust 2.1 |
| Road base, loose / compacted | 1.7 / 2.2 | 1.75 / 2.4 |
| Scoria | 1.0 | 1.0 |
| Compost | 0.6 | mulch and compost 0.6, humus 0.7 |
| Bark and wood-chip mulch | 0.35 | woodchip 0.4, bark 0.3 |
Most materials agree within about 10 %. Crusher dust is the exception, and it shows why the yard's own figure matters: the same name can cover a fine, dense screening and a coarser, lighter one. ANL itself calls its figures indicative, because density "may vary with grade, mineral content and moisture content". When the price is per tonne and the job is measured in cubic metres, ask the yard which figure they use, and use the custom density above.
Loose and compacted
Crushed rock and road base shrink when they are compacted with a plate compactor, so a tonne fills less volume in the finished base than it did loose on the truck. ANL gives road base 1.75 t/m³ loose and 2.4 compacted. GardenMaths uses 1.7 and 2.2. Order a base by the compacted figure: finished thickness × area × compacted density gives the tonnes to buy. Soil and mulch also settle after spreading, which is why the topsoil and mulch calculators add a settling allowance.
What it means for your trailer
Weight, not volume, limits a trailer. A typical 6 × 4 box trailer with a 750 kg ATM can legally carry about 500 kg. That is only 0.38 m³ of garden soil, or 1.4 m³ of bark mulch. A cubic metre of soil is three trips; a cubic metre of mulch fits in one. For anything over a cubic metre or two of heavy material, a delivery is usually cheaper than the fuel and the hours. The bagged vs bulk guide does the sums.
Conversion questions
How many tonnes is a cubic metre of soil?
About 1.2–1.4 tonnes, depending on the mix and how wet it is. GardenMaths uses 1.3 t/m³ for moist garden soil. ANL publishes 1.2 for garden mix and 1.4 for topsoil.
How many cubic metres is a tonne of gravel?
About 0.67 m³ at 1.5 t/m³, enough to cover 13 m² 50 mm deep. Denser products such as crushed sandstone or compacted road base give less volume per tonne.
How much does a cubic metre of sand weigh?
About 1.5 tonnes when dry to damp. ANL's figures range from 1.3 for Sydney sand to 1.5 for river sand, and wet sand is heavier.
How much does a cubic metre of mulch weigh?
About 0.3–0.4 tonnes for bark and wood chip, so a cubic metre of mulch is light enough for one trip in a 6 × 4 trailer, even though it fills it.
Sources and method
- Australian Native Landscapes, Landscape product weights and volumes – indicative densities for soils, sands, aggregates, mulches and soil conditioners.
- GardenMaths densities as used on the gravel, trailer load and paver calculators, compiled from Australian landscape-supply density tables.
- Trailer payload: a 750 kg ATM minus a typical 250 kg tare, as explained on the trailer load calculator.
Written by DueRiva · Last reviewed 24 September 2026 · Report an error