Blue metal is Australia’s go-to crushed aggregate — angular crushed basalt used for driveways, drainage and concrete. This calculator converts your measurements into cubic metres and tonnes using typical blue metal densities, with 20mm blue metal preselected.
How to use
- Measure your area in metres and enter the length, width and depth (a 300mm drainage trench = 0.3m deep).
- Pick your blue metal size — 20mm for drainage and driveways, 14mm for concrete, 7mm for paths.
- Keep the 10% extra ticked for compaction and wastage, then press Calculate.
Blue Metal Calculator
How much blue metal do you need? Enter your area below — results in cubic metres & tonnes.
Please enter valid numbers for length, width and depth.
Volume needed
Weight
20kg bags (approx.)
Estimates use typical bulk densities shown above. Actual density varies by supplier and moisture — confirm with your landscape supplier before ordering. How our calculators work
Frequently asked questions
What is blue metal made from?
Crushed basalt (bluestone) — a dense blue-grey volcanic rock quarried across Australia. Its angular shape locks together, which is why it compacts so well.
Which size blue metal should I use?
20mm for drainage, driveways and sub-base; 14mm or 10mm as concrete aggregate; 7mm for paths and decorative toppings.
How many tonnes is a cubic metre of blue metal?
About 1.5–1.6 tonnes depending on size — 20mm blue metal is typically 1.6 t/m³.