Work out how much rock, crushed aggregate, or river rock you need for landscaping, drainage and driveways — in tonnes and cubic metres, plus cost.
| Item | Value |
|---|
Crushed rock and gravel are essential materials in Australian construction and landscaping. They are sold by weight (tonne) or volume (m³) depending on the supplier.
| Application | Material | Depth |
|---|---|---|
| Driveway base | Crushed rock | 100 mm compacted |
| Drainage / French drain | 20 mm aggregate | Varies |
| Dry creek / feature | River rock | 100–150 mm |
| Erosion control | Rip rap | 150–300 mm |
| Garden feature | Mixed rock | 50–100 mm |
| Gravel Type | Bulk Density | Common Use |
|---|---|---|
| Pea gravel / river pebbles | ~1.5-1.6 t/m³ | Garden beds, decorative |
| Crushed rock (20mm) | ~1.8-1.9 t/m³ | Driveways, drainage |
| Blue metal (20mm) | ~1.9-2.0 t/m³ | Concrete aggregate, driveways |
| Decomposed granite | ~1.6-1.8 t/m³ | Paths, driveways |
| Road base (compacted) | ~2.0-2.2 t/m³ | Sub-base for driveways |
| Application | Recommended Depth |
|---|---|
| Decorative garden bed | 40-50 mm |
| Landscaping path | 50-75 mm |
| Residential driveway | 75-100 mm over compacted base |
| Drainage layer | 100-150 mm |
How do I calculate how much rock I need?
Multiply the area (length × width) by the depth, all in metres, to get cubic metres, then multiply by the rock density — usually 1.5–1.7 tonnes per cubic metre. The rock calculator above works this out and adds wastage. Rock is normally sold by the tonne.
How many tonnes of rock are in a cubic metre?
For most landscaping rock and crushed aggregate, one cubic metre weighs about 1.5–1.7 tonnes. Denser materials like road base can reach 1.8–2.0 t/m³, while lightweight scoria is closer to 1.0 t/m³. The calculator uses the density you select.
What size rock is best for drainage?
For drainage around pipes and French drains, 20 mm crushed aggregate is the common choice because water flows through it freely while it stays stable. Larger rock (40 mm+) suits soakwells and heavier drainage, and rip rap is used for erosion control on slopes and banks.