Gravel and aggregate guide for Australian projects
Road base — the workhorse aggregate
Road base (also called crushed rock, DGB-20 or Type 2 roadbase) is the standard sub-base for driveways, paths, paver beds and hardstands. It compacts to a dense, stable layer that drains well and doesn't shift under load. Standard depth is 75–100 mm compacted. Road base compacts about 20–25% from its loose volume — that's why this calculator uses a 15% waste margin as default.
Decomposed granite (DG)
Decomposed granite is a fine, golden-coloured aggregate popular for garden paths, courtyard surfaces and between stepping stones. Use 40–50 mm depth for foot traffic paths and 75 mm for driveways. Stabilised DG (mixed with a polymer binder) is available for higher-traffic areas.
River pebbles and garden pebbles
At 50–75 mm depth, river pebbles suppress weeds effectively and last indefinitely. Unlike organic mulch, they don't break down — but a geotextile underneath prevents them sinking into soil over time. Pebbles are sold by the tonne or in 25 kg bags; for areas over 5 m², bulk delivery is almost always cheaper.
Blue metal / bluestone
Crushed blue metal is the standard drainage aggregate behind retaining walls, in drainage trenches and as a sub-base for heavy traffic. For drainage, use 20 mm single-size washed (not crusher dust grade).
How bulk density affects your order
Landscape yards sell most aggregates by the tonne, not the cubic metre. Bulk density varies significantly — road base at 1.8 t/m³ is much heavier than garden pebbles at 1.4 t/m³ for the same volume. Always confirm the density with your supplier, as it varies by region and quarry.
Gravel and aggregate calculator — frequently asked questions
How much gravel do I need per square metre?
At 50 mm depth (standard for decorative gravel paths), you need 0.05 m³ per square metre. At 100 mm (road base or driveway base), it's 0.1 m³ per square metre. The calculator converts your area and depth to cubic metres and tonnes automatically.
How much does a cubic metre of gravel weigh?
Most gravel and aggregate in Australia weighs 1.4 to 1.6 tonnes per cubic metre. Decomposed granite is at the lighter end; crushed rock and road base sit toward the heavier end. The calculator uses material-specific densities for the tonnage figure.
What is the difference between road base and gravel?
Road base (also called DGB20 or crushed rock fines) is a compactable mix of crushed rock and fines — used as a structural base under driveways, paths and paving. Decorative gravel is washed, sorted by size and used for surface finish on paths and garden beds. They're not interchangeable — road base needs compaction, decorative gravel stays loose.
How deep should gravel be on a driveway?
For a residential driveway, 100 mm of compacted road base topped with 50 mm of compacted gravel surface is a standard specification. That's 150 mm total depth. On soft or sandy ground, increase the road base to 150 mm before adding the surface layer.
What gravel is best for garden paths in Australia?
Decomposed granite (DG) is popular for its natural look and ability to compact slightly underfoot. Pea gravel (10 mm round) stays loose and suits cottage-style gardens. Crushed sandstone suits Queensland gardens well and blends with the local palette. Avoid large (40 mm+) gravel on paths — it's uncomfortable to walk on and shifts underfoot.