The known weight units in the world of the Witcher are:
In The Witcher 3: Wild Hunt
Items in The Witcher 3 all have explicit weight statistics which factor into the total amount that Geralt can carry. Some common weights are listed below:
Alchemy ingredients 0 
Crafting components 0
Books 0
Food and drink 0 
Keys 0.01
Quest items 0.01
All other items have individual weights, and especially chest armor can be on the heavy side.
In The Witcher 2: Assassins of Kings
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
