How a concrete quantity is estimated

Wet volume is length × width × depth, with every side in metres. A slab 6 m by 4 m by 0.15 m is 3.6 m³ of concrete in place.

Dry materials

Concrete then multiplies that volume by 1.54 to allow for the voids in sand and coarse aggregate before they are mixed. Cement is counted in 50 kg bags, and each bag is taken as 0.035 m³. One cubic metre of a 1:2:4 mix is about 6.3 bags. Mortar and plaster do not use that 1.54 factor. They use 1.33, because they have no coarse aggregate.

This is a planning estimate. Confirm it against the drawings before you order. It is not a mix design.