The process description says further "corresponding to ca. 4.2 mm thickness" (of zinc). I am checking zinc coating, coils | zinc coat, coils | APOS, U RER in ei 3.7 but this is probably the same in ei 3.4. The product is zinc coating by galvanizing for 1 m², thus I think the total mass of your product does not matter. Rather you should consider the thickness of the zinc layer in your case (which you could maybe calculate from weight difference before and after the process, divided by the total area). If the zinc layer is thinner in your case, e.g. 3mm, multiply everything by 3/4.2.