Concrete Calculator
Work out how much concrete you need for a rectangular slab, footing or pad, in metric or imperial units.
How this is calculated
Volume = length × width × thickness × slab quantity, then increased by your waste percentage. We convert the result to m³, yd³ (× 1.30795) and ft³ (× 35.3147).
Bag counts are an estimate only, based on a yield you can edit. The default assumes roughly 0.011 m³ (0.4 ft³) of finished concrete per 30 kg bag — actual yield varies by product, so check the bag label.
Frequently asked questions
How much waste percentage should I add?
5% is a reasonable default for a simple slab poured by an experienced crew. Rougher subgrades, hand mixing or complex shapes often warrant 10% or more — adjust the field to match your job.
Does this account for reinforcement or forms?
No. This calculator only estimates concrete volume for the slab dimensions you enter. Rebar, mesh, formwork and finishing materials need to be estimated separately.
Why is my bag count only an estimate?
Bag yield depends on the specific mix and how much water is added. Always check the yield printed on your bag and update the assumption field if it differs from the default.
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