أنشئ حسابًا أو سجّل الدخول للانضمام إلى مجتمعك المهني.
Well, It's usually based on the operating experience of the organisation in the field of such projects. If the firm has previous experiences in handling such projects, it should definitely plans it's material requirements based on actual consumption and if it does not have any previous experiences, estimate the requirement.
What do you think?
