About these tools
Every quantity calculator makes assumptions, and the ones that hide them are the ones that send you back to the shop. Paint coverage varies by more than 30% between a matt emulsion and a gloss, and by more again over bare plaster. Flooring needs an offcut allowance that depends on the layout — a diagonal lay wastes roughly twice what a straight lay does. Tiles need more allowance again, because you break some.
So these tools show the allowance as a separate line rather than folding it into the total. You can see what the bare requirement is, what the waste factor added, and change it if your job is unusual — a small room full of awkward corners wastes more than a large empty one, and no default can know that.
The cooking converter is the one place where a confident answer would be wrong. Cups are a volume and flour is sold by weight, so converting between them requires a density that depends on the ingredient and on how it was measured — scooped flour can be 20% heavier than spooned. The tool gives the figure and the variance, and declines to guess for ingredients it does not have a density for.