As a rule, most weapons are about 2 to 4 pounds (about 1 or 2 kilos). It is such a truism, it seems pointless to actually track weapon weight in detail. Just estimate all weapons as if about 3 pounds each. Done.
As far as the game goes, it almost never matters, if the weight is 2 pounds or 3 pounds.
There seems no reason to track the weight.
Maybe “heavy weapons” weigh about 6 to 7 pounds (about 3 kilos). But that is pretty much the upper limit. With possible rare exceptions, any historical weapon heavier than this was “ceremonial”, looking cool when waving it in a parade, but unusable in battle. Heavy weapons include the German twohander great sword (bihänder, zweihänder), the Japanese great mace (kanabo, tetsubo), and so on.
• Weapon: about 3 pounds (±1)
• Heavy weapon: about 6 pounds (±1).
But there is no need to really care how much it weighs. Probably delete item weight from the weapon table to make the game feel cleaner and simpler.