Gravel and Aggregate Types for Australian Projects
Gravel and crushed rock are some of the most commonly ordered materials in Australian landscaping and construction. Whether you're building a driveway sub-base, laying a garden path, filling behind a retaining wall or creating a decorative garden feature, getting the quantity right before ordering saves both money and the hassle of a second delivery.
In Australia, aggregate is typically sold by the tonne for bulk orders (delivered by tipper truck) or by the cubic metre for smaller loads. Density varies significantly between material types, which is why our calculator converts volume to tonnes using the appropriate density for each material.
Common Aggregate Types and Their Uses
Pea Gravel / River Pebble (1.6 t/m³)
Smooth, rounded pebbles in 5–20mm sizes. Used for garden paths, drainage trenches, water features and decorative ground cover. Excellent drainage characteristics. Available in natural river pebble (cream, grey, brown tones) or coloured varieties. Pea gravel shifts underfoot, which makes it less suitable for driveways unless contained with edging.
Crushed Rock — 20mm (1.55 t/m³)
Angular crushed stone in 20mm nominal size. Excellent for drainage trenches (behind retaining walls, around drainage pipes) and as sub-base for paved areas. The angular shape means it locks together when compacted, unlike rounded gravel. Widely available from quarries across Australia.
Road Base / Crusher Dust (2.0–2.1 t/m³)
A blend of fine and coarse crushed rock that compacts to a hard, stable surface. The standard sub-base for driveways, paths, and paved areas. Road base is typically 20mm down (mixed sizes from 0–20mm) or crusher dust (0–5mm). Both need to be compacted with a plate compactor or vibrating roller. Properly compacted road base creates a foundation as solid as concrete for many applications.
Blue Metal Aggregate (1.5 t/m³)
Dark basalt or granite aggregate in various sizes (7mm, 10mm, 14mm, 20mm). Used in concrete mixes, drainage applications, and as a path surface. Blue metal 20mm with geotextile fabric beneath is a cost-effective driveway surface. Popular in bushfire zones because it won't burn.
Decomposed Granite (1.8 t/m³)
Partially weathered granite that breaks down into a finer texture than standard crushed rock. Compacts well, has a natural golden-brown colour, and drains effectively. Popular for garden paths, driveways in rural settings, and as a surface under pergolas. Affordable and widely available in eastern Australia.
Worked Example 1: Driveway Sub-Base
A 3m wide × 10m long driveway base using 150mm compacted road base:
- Area: 30m²
- Depth (allowing 20% compaction): 150mm × 1.2 = 180mm loose
- Volume: 30 × 0.18 = 5.4m³
- Weight at 2.0 t/m³: 10.8 tonnes
- Cost at $55/t + $120 delivery: approximately $714
Worked Example 2: Garden Path with Pea Gravel
A winding garden path 15m long × 0.9m wide at 75mm depth:
- Area: 13.5m²
- Volume: 13.5 × 0.075 = 1.01m³
- Weight at 1.6 t/m³: 1.62 tonnes
- Cost at $90/t + delivery: approximately $266
A small job like this is often cheaper to source in bulk bags (1 tonne bags, sometimes called "bulka bags") from a landscape supplier rather than ordering a full tipper load — though per-tonne cost is higher for bagged material.
Density Reference for Aggregates
The density of aggregate is crucial for converting between volume (m³) and weight (tonnes). Here are approximate densities for common materials:
- Pea gravel / river pebble: 1.6 t/m³
- Crushed rock 20mm: 1.55 t/m³
- Road base / crusher dust: 2.0–2.1 t/m³ (compacted)
- Blue metal: 1.5 t/m³
- Sand (coarse): 1.75 t/m³
- Decomposed granite: 1.8 t/m³
- Organic mulch: 0.35 t/m³
Compaction Factor: Don't Under-Order
Loose aggregate compacts when weight is applied — typically 10–15% for gravel and crushed rock, and up to 20–25% for road base and crusher dust. This means you need to order more than the finished depth calculation suggests. Our calculator applies a compaction/waste factor you can adjust, but 10–15% is appropriate for most jobs. Better to have a small amount left over than to run short mid-project.
Ordering Aggregate in Australia
For most residential jobs over about 1 tonne, ordering a tipper truck delivery from a local quarry or landscape supplier is the most economical approach. Most suppliers have minimum orders of 2–4 tonnes. For smaller amounts, bulka bags (0.75–1 tonne) from landscape suppliers or Bunnings are convenient and don't require you to be home for the delivery. For very small amounts, pre-bagged aggregate (20–25kg bags from Bunnings) is convenient but expensive per tonne.
5 FAQs About Gravel and Aggregate
50–75mm of compacted gravel is adequate for a lightly used garden path. For a more heavily used path or one that needs to support wheelbarrows or garden equipment, go to 100mm. For a gravel driveway that carries cars, 100–150mm of compacted road base covered with 50mm of decorative gravel is the standard approach.
For decorative garden paths and beds: yes, weed mat (geotextile fabric) is highly recommended under gravel. Without it, weeds will grow through within 1–2 seasons and the gravel will slowly mix into the soil. Use a quality needle-punched geotextile rather than the cheap woven plastic — it allows water through while blocking weeds and is much more durable.
Road base (or "DGB20" in Queensland) is a blend of 0–20mm crushed rock that includes a mix of fine and coarse particles for maximum compaction. Crusher dust (or "blue metal fines") is the fine residual from the crushing process — mostly 0–5mm — and compacts to an even harder surface. Both are used as sub-base material; crusher dust is often used as the final top layer under pavers or as a levelling bed.
It depends on the depth. At 50mm depth, one tonne of pea gravel (1.6 t/m³) covers approximately 12.5m². At 75mm depth, it covers about 8.3m². At 100mm, about 6.25m². For road base (2.0 t/m³), one tonne covers about 5m² at 100mm depth. Our calculator handles this automatically — enter your dimensions and it converts to tonnes for you.
Gravel driveways are popular in rural and semi-rural areas for their low cost and drainage characteristics. In urban settings they can be problematic — gravel migrates onto footpaths, blocks drains, and requires regular top-ups and raking. If you go with gravel, use angular crushed rock (not rounded pebbles) and install kerbing or steel edge strips to contain it. Many councils prohibit loose gravel driveways in urban areas because of the footpath and drain spillage problem.