How much gravel do I need?
Area times depth gets you the volume. Two things then decide whether the load that turns up is the right load: whether the material compacts, and what it weighs. Get either wrong and you're either short a tonne or you've ordered a truck you can't unload.
Compaction is the decision
Road base and crusher dust are graded so the fines fill the gaps between the stones. That's the whole point of them — under a plate compactor they lock together into something you can drive on. It also means they lose about 20 to 25% of their loose volume on the way there.
Washed gravel, river pebble and scoria have had the fines taken out, so there's nothing to migrate into the voids. They settle a little and that's it — allow 0 to 5%. Sand sits in between, and how much it drops depends more on how wet it is than on what you do to it.
The mistake is ordering the finished volume of road base. On a driveway that's a tonne or two short, which is a second delivery fee and a day lost waiting for it.
A worked example — a driveway
A 20m × 3m driveway, 150mm of compacted road base:
- Area: 20 × 3 = 60 m²
- Finished volume: 60 × 0.15 = 9 m³
- Plus 25% compaction: 9 × 1.25 = 11.25 m³ loose
- At road base's 2.1 t/m³: 11.25 × 2.1 = 23.63 tonnes
Lay that in two lifts of about 75mm rather than one 150mm dump. Wet each lift down and run the plate or the roller over it before the next one goes on — a single thick lift compacts on top and stays loose underneath, and that's where the ruts come from six months later.
A worked example — a pebble path
A 12m × 1m path, 75mm of river pebble over a compacted base, 5% allowance:
- 12 × 0.075 = 0.9 m³, plus 5% = 0.95 m³
- At 1.5 t/m³: 1.42 tonnes, or order 1 m³
Depths that actually work
| Job | Depth | Material |
|---|---|---|
| Decorative topping over a base | 50–75mm | River pebble, deco gravel |
| Garden or wheelbarrow path | 75–100mm compacted | Road base |
| Car driveway | 150mm compacted, in two lifts | Road base |
| Truck or heavy vehicle access | 200mm+ | Road base |
| Shed pad under a slab | 100mm compacted | Road base |
| Paver bedding | 25–30mm screeded, not compacted | Washed sand |
| Behind a retaining wall | 300mm wide zone, full height | 20mm washed, no fines |
| Ag-line trench | 100mm bedding + 150mm cover | 20mm washed, no fines |
Layering a driveway
A driveway that lasts is layers, not depth. Strip the topsoil and compact the subgrade. Over soft or clay ground, roll geotextile down first — it stops the base punching into the clay and disappearing. Then road base in lifts, compacted wet. Then a wearing course: 50mm of deco gravel, a seal, or pavers on 30mm of bedding sand.
Build fall into it while you're at it. Around 2% crossfall, or a crown down the middle, so water runs off instead of sitting in the base.
Drainage gravel: no fines, ever
Behind a retaining wall and around an ag-line you want 20mm washed aggregate — single-sized, clean, nothing fine in it. The voids between the stones are the drain. Backfill a wall with crusher dust instead and you've built a wall with no drainage: the fines pack, water sits behind it, and the pressure that wall was designed for goes up.
Wrap the drainage zone in geotextile so the surrounding soil can't wash into the voids and silt them up over a few wet seasons.
Bulk densities — and what a trailer really holds
| Material | Density | One tonne is | Covers at 100mm |
|---|---|---|---|
| Road base / crusher dust | 2.10 t/m³ | 0.48 m³ | 4.8 m² |
| Washed sand | 1.60 t/m³ | 0.63 m³ | 6.3 m² |
| Brickies sand | 1.55 t/m³ | 0.65 m³ | 6.5 m² |
| 20mm drainage gravel | 1.50 t/m³ | 0.67 m³ | 6.7 m² |
| River pebble | 1.50 t/m³ | 0.67 m³ | 6.7 m² |
| Scoria | 0.90 t/m³ | 1.11 m³ | 11.1 m² |
Road base is heavy, and a trailer holds far less of it than people think. A 6×4 box trailer takes about half a cubic metre level with the sides — but half a metre of road base is 1.05 tonnes. A common unbraked 6×4 is rated to 750kg all up, and after its own weight that's roughly 600kg of payload: under a third of a cubic metre, sitting maybe 130mm up the sides. Check the plate on the drawbar and the towball rating before you let the loader tip a bucket in.
Two more on weight. Densities move with the supplier and the moisture — wet sand runs 10 to 15% heavier, so ordering by the tonne after a week of rain means part of what you pay for is water. And brickies sand and washed sand aren't swappable: brickies sand is loamy so mortar handles nicely, washed sand is clean and sharp for bedding and concrete.
Quoting a gravel job
Material is the predictable half. Excavation, spoil removal, compaction hire and the number of barrow runs if the truck can't back in are what move the price. Quote the cart-away as its own line — 60 m² of driveway at 150mm is nine cubic metres of dirt out before a gram of base goes in.
Worked out the base. Now price the job.
Yamate turns your tonnes and hours into a quote the customer can accept on their phone, then an invoice, then a payment — with GST handled and the follow-ups chased for you.
Try Yamate free → Free to try · no card · sign in with a link, no password to rememberGravel, sand & aggregate FAQ
How much road base do I need for a driveway?
A 20m × 3m driveway at 150mm compacted is 9 cubic metres finished, about 11.25 loose once you allow 25% for compaction — roughly 23.6 tonnes. Enter your own size above.
How much does a cubic metre of road base weigh?
About 2.1 tonnes. That makes it the heaviest thing on this list — twice scoria and a third heavier than 20mm gravel. A tonne of road base is only 0.48 of a cubic metre.
How much extra should I order for compaction?
20 to 25% for road base and crusher dust, because the fines pack into the gaps. Washed gravel, river pebble and scoria have no fines to move, so 0 to 5% is plenty.
How deep should road base be under a driveway?
150mm compacted for cars, more for anything heavy, laid in two lifts of about 75mm and compacted wet. A single 150mm dump compacts on top and stays loose underneath.
What gravel goes behind a retaining wall?
20mm washed aggregate with no fines in it, in a zone about 300mm wide up the back of the wall, wrapped in geotextile. Crusher dust packs and holds water, which is the opposite of what a drainage zone is for.
How much gravel fits in a 6x4 trailer?
About half a cubic metre level with the sides — but weight stops you first. Half a metre of road base is over a tonne, and a common unbraked 6×4 is rated to 750kg all up. Check the plate.
Is gravel sold by the tonne or the cubic metre?
Quarry material like road base and aggregate is usually priced by the tonne, landscape material like pebble and scoria by the cubic metre. The calculator shows both so you can compare two suppliers quoting different ways.
Other calculators you'll want
General information for Australian trades, and an estimate only — not tax, financial or legal advice. It is not engineering, building or design advice either: a calculator works out a quantity from the figures you enter, and anything that needs sign-off still needs your engineer, certifier or building surveyor. Bulk densities are typical figures from Australian quarry and landscape suppliers and vary with grading, source and moisture — wet material weighs noticeably more. Confirm with your own supplier before ordering by weight. Pavement depths here are general trade practice; anything carrying vehicles over a soft or reactive subgrade should be designed for the site. This calculator is a materials estimate to help you order and quote, not an engineering specification.