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Concrete volume calculator

Slab dimensions in, cubic metres and bag count out — with a waste allowance.

Updated 3 Sept 2026
A freshly poured concrete slab inside timber formwork with cement bags and a tape measure beside it
A garden slab pour: the kind of job this calculator sizes. · Illustration

Enter the slab dimensions. Results update as you type.

Volume

1.18m³

With waste allowance
1.27m³
Bags to buy
113bags
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  • · Volumes assume a rectangular slab of uniform depth.
  • · Bag yield varies by product; check the figure printed on the bag.