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Enter your area and depth — we'll calculate exactly how many 1-tonne bulk bags you need, with the maths shown step by step.
| Depth | Volume / bag | Area covered |
|---|
To find how much material you need, multiply the area you want to cover by the depth of application. This gives you volume in cubic metres (m³).
Volume (m³) = Area (m²) × Depth (m)
Different materials have different bulk densities — how much a cubic metre of that material weighs. Mulch is mostly wood fibre and air, so it's very light (~0.25 t/m³). Sand and pebbles are solid mineral, making them much heavier (~1.5 t/m³). We multiply volume by density to get weight in tonnes.
Weight (t) = Volume (m³) × Bulk density (t/m³)
Each bag we sell is exactly 1 tonne, so the number of bags equals the weight in tonnes — rounded up to the next whole number (you can't buy half a bag). We also add a 10% buffer by default, because landscape materials compress slightly during delivery and lose a small amount during spreading.
Bags = ⌈ Weight × 1.10 ⌉
| Material | Density (t/m³) | Why? |
|---|---|---|
| Mulch & Bark | 0.25 | Wood fibre + air pockets — very light |
| Garden Soil | 0.85 | Loose blended mix of organics and minerals |
| Turf Underlay | 1.00 | Denser soil–sand blend |
| Sand | 1.50 | Compacted mineral — very dense |
| Decorative Pebbles | 1.45 | Solid stone aggregate |
These are typical industry values for the types of material we stock. Actual bulk density can vary slightly depending on moisture content and particle size.
Not sure which material is right for your project? Check our FAQ for coverage guides, or call us on 1300 872 267 and we'll help you work it out.
