Estimate the volume of concrete needed for a slab, footing or post hole, and how many bags to buy. Enter length, width and depth to get cubic metres, cubic yards and bag count.
Enter the length and width in metres and the depth in centimetres. The calculator returns the volume in cubic metres and cubic yards, and the number of bags required based on each bag's yield.
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A concrete calculator works out the volume of a rectangular pour so you order the right number of bags or ready-mix. Always round up and add a 5–10% safety margin for spillage and uneven ground.
A typical 25 kg bag of pre-mixed concrete yields about 0.0125 m³ (12.5 litres).
5–10% is standard to cover spillage, uneven sub-base and minor measurement errors. For larger pours, ready-mix delivered by truck is usually more economical than bags.
It varies by bag size and mix. A 25 kg bag of general-purpose concrete yields roughly 0.0125 m³; a 40 kg bag about 0.02 m³. Check the manufacturer's figure and set it in 'Yield per bag'.