Groundwork and masonry
Concrete, aggregates, bricks and blocks, measured by volume or by area.
Concrete
The concrete calculator, under “Job calculators” on the all calculators page, works out the concrete for one slab, path or shed base of even thickness. You enter the thickness; it gives whole bags from the yield on the bag, or cubic metres to order, with the sub-base, a membrane, reinforcement and formwork left as checks.
What these have in common
Unlike paint or flooring, these are usually ordered by volume or weight rather than by the pack, and the conversion between the two depends on the material. A cubic metre of one aggregate does not weigh the same as a cubic metre of another, and the figure changes with how wet it is.
Where a calculator here needs a density or a yield, it asks for it rather than assuming one, and says where a sensible figure can be found.
These are not design tools
They work out how much material a shape needs. They do not tell you what the shape should be. Foundation depths, slab thicknesses, reinforcement, lintels and anything structural need a qualified designer and, usually, building control approval.