The known weight units in the world of the Witcher are:

• Hundredweight - weight unit of 100 Pounds
• Pound - weight unit of 2 Marks
• Mark - weight unit of (presumeably) 8 Ounces
• Ounce - weight unit (presumeably) ca. 30g weight
• Lot - weight unit of (presumeably) ½ Ounce

In The Witcher 2: Assassins of Kings Edit

Items in The Witcher 2 all have explicit weight statistics which factor into the total amount that Geralt can carry. Some common weights are listed below:

books	0
quest items	0
crafting diagrams	0.1
potions	0.2
oils	0.2
bombs	0.5