To calculate how much concrete you need: multiply the length (m) × width (m) × depth (m) to get your volume in cubic metres (m3), then add 10% for waste. That is the core formula and the rest of this guide gives you worked examples for the most common residential projects, plus the common mistakes that leave people short on pour day.
The Basic Formula
Volume (m3) = Length (m) × Width (m) × Depth (m)
For example: a driveway that is 12m long, 3m wide, and 0.1m (100mm) deep = 12 × 3 × 0.1 = 3.6m3. Add 10% buffer → order 4m3.
This formula works for any flat rectangular pour: driveways, slabs, paths, shed floors, and pool surrounds. For irregular shapes, break the area into rectangles, calculate each, and add them together.
Worked Examples for Common Projects
Single-Car Driveway
Dimensions: 6m long × 2.8m wide × 100mm (0.1m) deep. Calculation: 6 × 2.8 × 0.1 = 1.68m3. Add 10%: order 1.85m3, round up to 2m3. This is a small pour well-suited to Broadmix’s mini mix service.
Double-Car Driveway
Dimensions: 10m long × 5.5m wide × 100mm deep. Calculation: 10 × 5.5 × 0.1 = 5.5m3. Add 10%: order 6.05m3, round up to 6.5m3. Standard transit mixer territory.If you are planning an exposed aggregate driveway, the volume calculation is the same, only the mix changes.
House Slab (Small)
Dimensions: 10m long × 8m wide × 100mm deep. Calculation: 10 × 8 × 0.1 = 8m3. Add 10%: order 8.8m3, round to 9m3. Note: house slabs often have engineered thicknesses — always check your plans for the specified depth before ordering.
Post Footings / Stumps
For a cylindrical footing: volume = π × radius² × depth. For a 300mm diameter (0.15m radius) footing at 600mm (0.6m) deep: 3.14 × 0.0225 × 0.6 = 0.042m3 per footing. If you have 20 footings: 20 × 0.042 = 0.85m3 + 10% buffer = approximately 1m3.
Why the 10% Buffer Rule Matters
Every site has variability. Subbase surfaces are rarely perfectly level, formwork depth can vary by a few millimetres across a long pour, and some concrete is always wasted in placement. Running short mid-pour is one of the worst things that can happen cold joints (where fresh and semi-set concrete meet) are weak points and very difficult to make disappear cosmetically.
Always order at least 10% more than your calculation. For large or complex pours, 15% is not excessive. The cost of a small surplus is far less than the cost of a cold joint or a shortfall call to your supplier.This is one of the reasons working with a local Central Victoria supplier matters, because shorter delivery distances mean a top-up truck can reach your site faster if you do come up short.
Depth Reference Guide for Common Applications
Use these as a starting point, but always confirm with your building plans or engineer for structural applications.
- Driveways (residential): 100mm standard, 125mm for heavy vehicles
- House slabs: 100mm minimum (structural designs vary widely)
- Garden paths: 75 to 100mm
- Shed bases: 100mm
- Pool surrounds: 100mm
- Retaining wall footings: as per engineering spec
- Permeable concrete driveways: 100 to 150mm depending on subbase
Frequently Asked Questions
How many cubic metres of concrete does a standard driveway need?
A double-car residential driveway (approximately 40–50m2 at 100mm depth) requires approximately 4 to 5m3 of concrete including a 10% buffer. A single-car driveway (approximately 15–20m2) requires approximately 1.7 to 2.2m3. These are estimates calculate your specific dimensions for accuracy.
How much concrete does a concrete truck hold in Australia?
A standard transit mixer truck in Australia typically carries between 5m3 and 8m3 of concrete. Mini mix trucks carry between 0.5m3 and 3m3. Broadmix operates both types the right vehicle for your project depends on your volume and site access.For tight residential sites in Wallan, Kilmore, mini mix is often the smarter option.
What happens if I underestimate how much concrete I need?
Running short mid-pour forces you to either pause and wait for more concrete during which the first pour begins to set, creating a cold joint or abandon part of the pour and patch it later. Both outcomes produce a structurally weaker result and are visually difficult to hide. Always calculate conservatively and include your buffer.
Can Broadmix help me calculate how much concrete I need?
Yes. Call us with your project dimensions and we will work through the volume calculation with you, confirm the right mix, and advise on the best delivery option. We do this for every residential customer it is part of the service. Get in touch with our Broadford depot to chat through your numbers.
Order the Right Amount — Talk to Broadmix
Broadmix supplies premix concrete, exposed aggregate, and permeable concrete across Central Victoria. Whether you have your volume ready or you need help working it out, call us at our Broadford depot or visit broadmix.com.au. We will make sure you order the right amount and the right mix for your project.
