Concrete Calculator
Volume and bags for slabs and footings
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About this calculator
Enter the length, width and thickness to get the volume, with an allowance for waste and spillage. The bag counts use typical yields for ready-mix bags.
The formula
Volume = length × width × thickness (+ waste %)
Worked example4 m × 3 m × 10 cm = 1.2 m³; with 10% waste, 1.32 m³.
Frequently asked questions
How much extra should I order?
Add 5–10% for waste, uneven ground and spillage.
How many bags per cubic metre?
About 80 bags of 25 kg or 50 bags of 40 kg per m³ of mixed concrete.
Does it include reinforcement?
No. Mesh and rebar take little volume but need ordering separately.
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