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Concrete Calculator (Cement, Sand & Aggregate)
Work out how much concrete a slab, footing or column needs and how many bags of cement, and how much sand and aggregate, to order for a nominal mix.
How this is calculated
Wet volume is converted to dry volume with the standard factor of 1.54, then split by the mix ratio: M10 = 1:3:6, M15 = 1:2:4, M20 = 1:1.5:3, M25 = 1:1:2.
Cement volume is converted to bags using a density of 1,440 kg/m³ and 50 kg bags. Water uses a water–cement ratio of 0.5. A wastage allowance is added to every quantity.
Frequently asked questions
How many cement bags are needed for 1 cubic metre of M20 concrete?
About 8 bags (8.06) for a nominal 1:1.5:3 mix, before wastage.
Should I use a design mix instead?
For M25 and above, and for any structural work on multi-storey buildings, use a design mix specified by your structural engineer or ready-mix supplier. Nominal mixes are fine for estimating.
Estimates are for planning only. Prices vary by city, brand, design and site conditions — get itemised quotes before you commit.