Concrete Calculator

Concrete volume for a slab or footing, the weight, and the cement, sand and aggregate to mix it yourself.

Length mm

The longer dimension of the slab, footing or pad.

Width mm

The other dimension, at right angles to the length.

Thickness mm

75 to 100 mm for a path, 100 to 150 mm for a shed base. A slab that carries a vehicle needs a thickness that has been specified.

Waste allowance %

Five per cent on a flat slab over a prepared base, ten per cent in a rough trench or over hardcore.

Cement part

The first number of the mix ratio. A 1:2:4 mix uses 1 part cement.

Sand part

The middle number of the mix ratio. Sharp sand is the usual fine aggregate.

Coarse aggregate part

The last number of the mix ratio. 20 mm crushed stone is the usual coarse aggregate.

Dry volume factor times

Loose sand and stone contain air that the cement paste fills, so the dry ingredients bulk up. The standard allowance is 1.54 times the wet volume.

Bulk density of cement kg/m3

Turns the volume of cement into the weight the bag is sold by. About 1440 kilograms per cubic metre for ordinary Portland cement.

Cement bag size kg

25 kg is the common bag in the UK and Europe, 50 kg in the US, and 20 kg in some ranges.

Price per bag of cement

Optional. Used for the cement cost only, not for the sand or the stone.

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Free calculator by Handcraft worked examples and methodology No account, nothing stored.