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How much concrete for a 3×3 m slab at 125 mm thick?
You'll need about 1.18 m³ of concrete for this slab, including a 5% wastage allowance — that's roughly 110 × 20 kg premix bags if you're not ordering pre-mixed.
At this volume, bagged premix is a practical DIY option — budget real time for mixing this many bags by hand.
| Slab size | 3 m × 3 m |
|---|---|
| Thickness | 125 mm |
| Waste allowance | 5% |
| Concrete volume | 1.18 m³ |
| 20 kg bags | 110 |
| Approx. mass | 2.84 t (@ 2.4 t/m³) |
Assumptions
- 5% wastage allowance, the /site/materials calculator default.
- 20 kg premix bags yield about 0.0108 m³ each.
- Volume only — excludes reinforcement (mesh), formwork, base preparation and any fall/thickening at edges.
Check before you order: Confirm reinforcement (mesh/reo), site access for a mixer truck, and the exact thickness with your slab supplier or engineer before ordering — this figure is volume only.
How this is worked out & FAQ
How this is worked out
- Multiply length × width × thickness (in metres) for raw volume.
- Add the waste allowance.
- Divide by 0.0108 m³ per 20 kg bag and round up, if using bags.
FAQ
Should I order bags or a truck?
At this volume, bagged premix is usually practical, though it's worth a quick delivered quote for comparison if you're short on time.
Does this include reinforcement mesh?
No — this is concrete volume only. Use the Reo mesh calculator on /site/materials for SL-mesh sheet counts separately.
What about edge thickening or footings?
Not included — this assumes a uniform slab thickness. Add extra volume separately for any thickened edges or integrated footings.
Estimates only — allow for laps, cuts and site conditions. ← more concrete volume · All material calculators