How we work it out
Length × width × depth gives cubic metres, the same sum as concrete or mulch. Multiply that by the material's density and you get tonnes, the unit every landscape yard actually sells by, since loose gravel, crusher dust and decorative pebbles all pack to a different weight per cubic metre depending on how heavy and how angular the stone is.
Worked example: a 6 m × 3 m driveway strip (18 m²) at 75 mm needs 1.35 m³ of blue metal, which at 1.4 tonnes per cubic metre works out to about 1.9 tonnes. Delivered in bulk that's roughly $190 to $255. Buying the same 1.9 tonnes in 20 kg bags means carrying home 95 of them, at around $760, about four times the bulk price for identical gravel.
Which material?
Blue metal (crushed basalt or similar hard rock) is the default for driveways, drainage lines and general fill, angular, load-bearing and cheap relative to decorative stone. Crusher dust is finer and compacts harder, which is why it's the standard bedding layer under pavers and slabs rather than a driveway surface on its own. Decorative pebbles, river pebbles, white stone and similar, cost several times as much per tonne as either, since they're selected and often washed for colour and shape rather than crushed for strength, and they're doing a garden-bed or feature job, not a structural one.
Bulk or bags?
Per kilo, bagged gravel from a hardware or garden shop typically runs three to six times what the same material costs delivered in bulk from a landscape yard, a 20 kg bag of blue metal at $8 works out to $400 a tonne, against $100 to $135 delivered loose. Bulk suppliers commonly apply a minimum order or a small-load delivery fee below roughly half a tonne to a tonne, which is the one thing that can tip a small job back toward bags despite the higher unit price.
Common questions
How many tonnes of gravel do I need?
Multiply length by width by depth in metres to get cubic metres, then multiply by the material's density: about 1.4 tonnes per cubic metre for blue metal, 1.6 for crusher dust, 1.5 for decorative pebbles.
How deep should a gravel driveway be?
75 mm is a standard topping depth for a path or light driveway over a compacted base, rising to 100–150 mm where the base itself needs to carry vehicle weight.
Is it cheaper to buy gravel in bulk or in bags?
Bulk, by a wide margin, typically a third to a sixth of the bagged price per kilo. Bags mainly make sense for very small jobs, since most bulk suppliers apply a minimum order or delivery fee below roughly half a tonne to a tonne.
Do I need a weed membrane under gravel, and does it change the quantities above?
It doesn't change the tonnes or bags above: a membrane sits underneath the gravel layer rather than adding to it, and its job is stopping soil rising up into the gravel and the gravel sinking into softer ground, not stopping weeds on its own. A budget mat is rated for only 2 to 4 years and works out pricier once you count relaying labour, while a heavier fabric costs more upfront but usually wins over a decade.
Sources
Electricity rates: AER Default Market Offer (NSW, SA, south-east QLD), Victorian Default Offer, and each remaining state's regulated tariff, current for 2026–27. Appliance figures: the energyrating.gov.au registration database (July 2026 snapshot). Methods and assumptions are described on each page.