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BetaConcrete Calculator for Australian Pours
Calculate concrete volume in m³, 20kg bags, waste allowance and indicative pour cost for Australian slabs, driveways, footings and DIY or trade jobs.
Pour plan
Start with your project
Pick the closest match. We’ll show only the measurements and advice that matter for that pour.
Common pours
Tap one to continueMore shapes & specialist poursCrossover, stairs, kerbs and round work
Measure once, order sensibly
How the volume estimate works
The calculator converts every input to metres, applies the correct geometry for your project, adds your chosen waste allowance, then rounds the recommended order to the next 0.2m³. It keeps indicative planning costs separate from live supplier quotes.
Worked example
A 5m × 4m slab at 100mm deep. Convert the depth to metres first: 100mm ÷ 1000 = 0.1m.
- Volume
- 5 × 4 × 0.1 = 2.00 m³
- Plus 10% waste
- 2.20 m³
- Order this much
- 2.20 m³
- Or in 20kg bags
- 238 bags
Ready-mix is ordered in 0.2m³ steps, so the recommended order rounds up to the next step.
Concrete volume formulas
These are the formulas the calculator uses. Convert every measurement to metres before multiplying.
| Project | Formula |
|---|---|
| Slabs, driveways, paths, patios, crossovers, kerbs | length (m) × width (m) × depth (m) |
| Strip footings | length (m) × width (m) × depth (m) |
| Round piers or post holes | π × (diameter ÷ 2)² × depth (m) × number of holes |
| Square piers | width (m)² × depth (m) × number of piers |
| Round pours and columns | π × (diameter ÷ 2)² × depth (m) |
| Stairs | width (m) × tread (m) × riser (m) × (steps × (steps + 1) ÷ 2) |
| Pool surrounds and other subtractive areas | (total area − pool area) (m²) × depth (m) |
Common Australian pours
Typical jobs with 10% waste added and the 20kg bag equivalent. These are planning references, not recommended structural dimensions — confirm depth, strength and reinforcement with your concreter or engineer.
| Project | Dimensions | Volume | +10% waste | 20kg bags |
|---|---|---|---|---|
| Single garage slab | 6m × 3m × 100mm | 1.80 m³ | 1.98 m³ | 214 |
| Double driveway | 12m × 3m × 100mm | 3.60 m³ | 3.96 m³ | 428 |
| Patio | 4m × 4m × 100mm | 1.60 m³ | 1.76 m³ | 191 |
| Garden path | 10m × 1m × 75mm | 0.75 m³ | 0.83 m³ | 90 |
| Fence post holes | 10 holes, 300mm dia × 600mm | 0.42 m³ | 0.47 m³ | 51 |
Why you order more than you measure
Concrete is lost to spillage, uneven formwork and over-excavation, and running short mid-pour is far more expensive than a little spare. The waste allowance is a planning assumption, not a measurement:
- 5% — precise formwork, experienced crew, flat prepared base.
- 10% — the usual allowance for residential work.
- 15% — irregular shapes, rough excavation, or a first DIY pour.
Bags or ready-mix?
One cubic metre is roughly 108 × 20kg bags, which is a lot of mixing. Bagged concrete suits small pours under about 0.5m³ — post holes, a small landing, a repair. Beyond that, ready-mix is cheaper per cubic metre and dramatically faster.
Small loads usually attract a short-load fee because the truck and driver cost the same regardless of how full it is.