What this calculator does
Road base is a compacted layer of crushed rock and aggregate laid underneath driveways, paths and pavers to give a firm, stable base before the finished surface goes down. This road base calculator works out the volume and weight needed from the area to be covered and the compacted depth, so you know how much to order.
Because road base density varies by the exact material, moisture content and how much it is compacted, this calculator leaves density as an editable input rather than a fixed number. A commonly cited range is roughly 1.6 to 2.2 tonnes per cubic metre, but check the figure your supplier quotes for the specific product, since "road base calculator Australia" searches usually turn up quarry-specific numbers that differ from a generic average.
The formula
Volume is length times width times depth, with the depth converted from millimetres to metres by dividing by 1,000. Weight in tonnes is that volume multiplied by the density you enter. Bags needed rounds up the weight in kilograms divided by the bag size, and cost multiplies the tonnage by a price per tonne.
| Term | Meaning |
|---|---|
| Volume | Length × width × (depth ÷ 1,000), in cubic metres. |
| Density | The weight of one cubic metre of compacted road base, in tonnes per cubic metre. This varies by material and must be checked against your supplier, not assumed. |
| Weight | Volume × density, the tonnage to order. |
The inputs explained
| Field | What to enter |
|---|---|
| Area length (m) | The length of the area to be covered. |
| Area width (m) | The width of the area to be covered. |
| Compacted depth (mm) | The compacted depth of the road base layer, in millimetres. A typical driveway sub-base is often 100 to 150 mm, but check local requirements. |
| Road base density (t/m³) | The density of your specific road base material, in tonnes per cubic metre. Ask your supplier rather than guessing; this figure genuinely varies. |
| Bag size (kg) | The size of the bags you plan to buy, if buying bagged rather than bulk. |
| Price per tonne ($) | The price charged per tonne, for an estimated total cost. |
When to use it
Quoting a driveway job
Working out road base tonnage from the driveway’s dimensions and the required compacted depth gives a defensible order quantity before ordering a bulk delivery.
Buying bagged road base for a small path
For a small garden path where bulk delivery is not practical, converting the tonnage into a bag count at a given bag size shows how many bags to buy.
Comparing supplier quotes
Different quarries quote road base at different densities and prices per tonne; running the same area and depth through each supplier’s numbers puts the quotes on the same footing.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much road base is needed for different driveway lengths?
A 3 m wide driveway at a 100 mm compacted depth, across a range of lengths.
| Driveway length | Road base needed | Volume required |
|---|---|---|
| 5 m | 2.850 tonnes | 1.500 m³ |
| 8 m | 4.560 tonnes | 2.400 m³ |
| 10 m | 5.700 tonnes | 3.000 m³ |
| 15 m | 8.550 tonnes | 4.500 m³ |
| 20 m | 11.400 tonnes | 6.000 m³ |
| 30 m | 17.100 tonnes | 9.000 m³ |
How tonnage changes with compacted depth
A fixed 10 m by 3 m area, across a range of compacted depths.
| Compacted depth | Road base needed | Volume required |
|---|---|---|
| 50 mm | 2.850 tonnes | 1.500 m³ |
| 75 mm | 4.275 tonnes | 2.250 m³ |
| 100 mm | 5.700 tonnes | 3.000 m³ |
| 125 mm | 7.125 tonnes | 3.750 m³ |
| 150 mm | 8.550 tonnes | 4.500 m³ |
| 200 mm | 11.400 tonnes | 6.000 m³ |
Questions
What compacted depth of road base do I need for a driveway?
It depends on the sub-grade soil and what will drive over it, and local building guidance is the authority on this, not a generic rule. Once you have a target depth, this calculator turns it into a tonnage.
Why is the density figure not fixed in this calculator?
Road base density genuinely differs between quarries and product types, and depends on how well it is compacted on site. Using a fixed number would understate or overstate the order for a lot of real materials, so it is left as an editable input; check the figure your supplier quotes.
Does this account for compaction shrinkage?
No. The volume calculated here is the finished, compacted volume at the depth you enter; some suppliers separately note that loose (uncompacted) material takes up more volume before it is compacted down, so ask your supplier whether their quoted tonnage already assumes compaction.
Should I order extra to allow for waste?
Many tradespeople add a margin, commonly around 5 to 10%, to cover an uneven sub-grade or minor spillage. That is a judgement call for the specific site, not something this calculator adds automatically.
For a similar volume-and-weight calculation on a different material, see the gravel calculator or the concrete weight calculator.