Landscape materials are sold in a confusing mix of units: cubic metres for bark and soil, tonnes or bulk bags for aggregates, and handy bags in litres or kilograms. Everything starts from the same volume calculation.
Volume first
volume = area × depth. Convert depth to metres before multiplying: 50 mm is 0.05 m.
Weight from volume
| Material | Approx. density |
|---|---|
| Crushed stone / gravel | 1.5–1.7 t/m³ |
| Sand (dry) | 1.5–1.6 t/m³ |
| Topsoil | 1.2–1.4 t/m³ |
| MOT Type 1 (compacted) | 2.0–2.2 t/m³ |
| Bark | ~0.35–0.45 t/m³ |
Wet material is heavier, often by 10–20%.
What a bulk bag covers
A bulk bag of gravel (~850 kg, about 0.55 m³) covers roughly 11 m² at 50 mm. A 1 m³ bag of bark covers about 13 m² at 75 mm.
Bags vs bulk
A cubic metre is about 14 bags of 70 L bark, or about 64 bags of 25 kg gravel. Bulk bags are usually cheaper above half a cubic metre, if the lorry can reach.
Compaction and settling
Base materials compact by 15–25%, and loose soil settles 15–20%. Add these allowances to the volume, or you'll come up short.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the Building Regulations and Building Control for your project.