Enter your slab or footing size to get the volume in cubic metres and the number of bags — with waste included.
This concrete calculator tells you how much concrete you need for a slab, path or footing. The volume is length × width × thickness in cubic metres; add a waste allowance (around 10%) for spillage and uneven ground. For bagged mix, the tool divides the volume by the yield per bag — a 25 kg bag makes roughly 0.011 m³ — to give the number of bags to buy.
Small jobs are easy with bags; once you pass about 0.5–1 m³, ordering ready-mix is usually cheaper and faster than mixing dozens of bags by hand. Either way, order slightly over rather than run out mid-pour — a cold joint from a delayed second batch weakens the slab.
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