Work out how much rock, crushed aggregate, or river rock you need for landscaping, drainage and driveways — in tonnes/m³ (metric) or tons/cubic yards (US), with cost.
Enter your area and rock depth below and pick your units — the calculator works out the volume and weight of rock you need, plus an estimated cost, whether you buy by the tonne (AU) or the cubic yard (US).
| Item | Value |
|---|
Crushed rock and gravel are essential materials in Australian construction and landscaping. They are sold by weight (tonne) or volume (m³) depending on the supplier.
| Application | Material | Depth |
|---|---|---|
| Driveway base | Crushed rock | 100 mm compacted |
| Drainage / French drain | 20 mm aggregate | Varies |
| Dry creek / feature | River rock | 100–150 mm |
| Erosion control | Rip rap | 150–300 mm |
| Garden feature | Mixed rock | 50–100 mm |
For a driveway base 12 metres long and 3 metres wide at 100 mm deep, the area is 12 × 3 = 36 m². Volume is 36 × 0.10 = 3.6 m³. Using crushed rock at 1600 kg/m³, that’s 3.6 × 1600 = 5760 kg, or about 5.76 tonnes. With 10% added for compaction and wastage, you’d order around 6.3 tonnes.
Landscaping rock does more jobs than most people realise, and matching the rock to the task saves money. For driveways, a compacted crushed-rock base topped with a finer aggregate gives a durable, well-draining surface. For drainage — French drains, soakwells, and around ag-pipe — 20 mm washed aggregate is the standard because water moves through it freely without washing away fines. Larger rip-rap and rubble are used on slopes and creek banks to control erosion, where the weight of the individual rocks resists being moved by water.
River rock and decorative pebbles serve a different purpose, used for dry creek beds, feature borders, and low-maintenance garden areas where you want ground cover without planting. When ordering, remember rock is sold by the tonne but delivered loose, so allow space for the pile and order a little extra — it’s far cheaper to have a small surplus than to pay a second delivery fee for the last quarter-tonne. Laying geotextile fabric underneath any decorative rock stops it mixing into the soil and keeps weeds down, which dramatically extends how long the job looks good.
| Gravel Type | Bulk Density | Common Use |
|---|---|---|
| Pea gravel / river pebbles | ~1.5-1.6 t/m³ | Garden beds, decorative |
| Crushed rock (20mm) | ~1.8-1.9 t/m³ | Driveways, drainage |
| Blue metal (20mm) | ~1.9-2.0 t/m³ | Concrete aggregate, driveways |
| Decomposed granite | ~1.6-1.8 t/m³ | Paths, driveways |
| Road base (compacted) | ~2.0-2.2 t/m³ | Sub-base for driveways |
| Application | Recommended Depth |
|---|---|
| Decorative garden bed | 40-50 mm (1.5-2 in) |
| Landscaping path | 50-75 mm (2-3 in) |
| Residential driveway | 75-100 mm (3-4 in) over compacted base |
| Drainage layer | 100-150 mm (4-6 in) |
Rock and aggregate are measured differently depending on where you're buying. Australian quarries and landscape suppliers price by the tonne and quote volume in cubic metres (m³). US rock and gravel yards price by the cubic yard and weigh loads in US (short) tons. Use the Metric/US toggle above the calculator to switch instantly.
| Measure | Australia / Metric | United States |
|---|---|---|
| Volume unit | Cubic metre (m³) | Cubic yard (cu yd) |
| Weight unit | Tonne (1,000 kg) | US ton / short ton (2,000 lb) |
| Conversion | 1 m³ = 1.308 cu yd | 1 cu yd = 0.765 m³ |
| Conversion | 1 tonne = 1.102 US tons | 1 US ton = 0.907 tonnes |
| Typical yield | ~1.5-1.9 tonnes per m³ | ~1.2-1.6 US tons per cu yd |
How do I calculate how much rock I need?
Multiply the area (length × width) by the depth to get volume, then multiply by the rock's density — usually 1.5–1.9 tonnes per cubic metre (about 1.2–1.6 US tons per cubic yard). The rock calculator above works this out automatically in either metric or US units and adds a wastage allowance.
How many tonnes (or tons) of rock are in a cubic metre/yard?
For most landscaping rock and crushed aggregate, one cubic metre weighs about 1.5–1.9 tonnes, or roughly 1.2–1.6 US tons per cubic yard. Denser materials like road base sit at the top of that range, while lightweight scoria is much lower. The calculator uses the density you select.
What size rock is best for drainage?
For drainage around pipes and French drains, 20 mm (¾ in) crushed aggregate is the common choice because water flows through it freely while it stays stable. Larger rock (40 mm / 1.5 in+) suits soakwells and heavier drainage, and rip rap is used for erosion control on slopes and banks.
How do I stop rock sinking into the soil?
Lay a geotextile (weed-mat) fabric over the soil before spreading the rock. It separates the rock from the ground, stops the two mixing over time, and suppresses weeds — keeping your coverage depth intact for far longer.
What size rock is best for a driveway base?
Crushed rock or road base around 20–40 mm (¾-1.5 in), laid about 100 mm (4 in) deep and compacted in layers, gives a firm, well-draining driveway foundation. Finer material can be used as a top dressing.
How many cubic yards of rock do I need?
Switch the calculator to US units, enter your area in feet and depth in inches, and it converts straight to cubic yards. As a rule of thumb, one cubic yard covers about 80-100 sq ft at 3-4 in deep for most crushed rock.
How much extra rock should I order?
Add about 10% to your calculated amount for wastage, spreading losses and compaction. Since rock is delivered loose, a small surplus is cheaper than paying a second delivery fee for a fraction of a load.