Concrete Volume Calculator
Work out how much concrete you need for a slab, base or footing, volume in m³, the number of 25kg bags, and an indicative ready-mix delivered cost.
Estimate only. This is an indicative estimate, not a quote. Confirm exact quantities and pricing with your builders' merchant or ready-mix concrete supplier before ordering.
Enter your slab dimensions
Your concrete volume, bag count and ready-mix cost appear here as you type.
How concrete volume is calculated
The raw volume is simply length x width x depth, converted to cubic metres. We then add a 10% wastage allowance on top, the standard rule of thumb that covers uneven ground, over-dig and spillage during the pour, so you don't run short partway through. From that final volume, we estimate two useful quantities: the number of 25kg bags of pre-mixed concrete you'd need (each bag yields around 0.011 m³ once mixed with water), and an indicative cost if you order ready-mix concrete delivered by lorry instead, usually the better option above around 1-2 m³. Always round up when buying bags, and confirm minimum order quantities and exact pricing with your supplier before ordering.
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