How much material
will the job take?

Pick the product, then what you want out of it. Weight for a size, length for a coil, rolls for a run, or the reinforcement a member is likely to take. The arithmetic is the arithmetic the trade uses, so it is good enough to plan and to ask us a sensible question with. It is not a structural design.

Everything we supply is billed on weight, whatever shape it arrives in, so the kilogram is the figure a price is applied to. That is why this works in weight throughout, and why the tolerance each standard allows is named beside the answer: it is the band the delivered weight, and so the bill, can sit in.