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.