Cement calculator

How many 50 kg cement bags, and how much sand and aggregate, for a slab, footing or beam. Enter the size and the concrete mix.

Changed units? Re-enter the sizes in the new units before calculating.

How it is calculated

1. Wet volume = length × width × thickness (in m³).
2. Dry volume = wet volume × 1.54. Dry cement, sand and aggregate have air gaps that disappear once water is added, so you need about 54% more dry material.
3. Cement = dry volume × cement share of the mix (for M20, 1 ÷ 5.5).
4. Cement weighs about 1440 kg/m³, so bags = cement m³ × 1440 ÷ 50, rounded up.

Which mix should I use?

Nominal mixes are the traditional site proportions: M10 (1:3:6) for levelling and non-structural PCC, M15 (1:2:4) for PCC under footings and floors, and M20 (1:1.5:3) for reinforced slabs, beams and columns in houses. Anything your structural engineer specifies — including design mixes of M25 and above — takes priority over this estimate.

Is this exact?

It is an ordering estimate. Real consumption varies with sand moisture, compaction and handling, which is why the 5% extra figure is shown. For slabs thicker at the edges, or sloped roofs, calculate each part separately and add them.

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