Weight Classes configuration
Important to understand the meaning of weight classes in different admin areas.
Base Weight Class: used for conversion from weight class set in the product (Base class set in System → Localization → Weight Classes)
Store's Weight Class: Change this class if you want to display cart weight in different weight units. If you have multi-stores you may want to show your Default store's customers weight in kilograms and show in another store same weight but in pounds. (Set in System → Settings → Store Details)
Product's Weight Class: The unit of the weight set in the product. Say you can have product's weight 500 and set Product's weight class to grams or you can set the same product to be 0.5 weight in kilograms. In both cases, the total weight of customer's basket will not be changed and recalculated infraction of Base weight class. And will be displayed in the Store weight class set in store settings
Delivery method's Weight Class (if available): some shipping extensions may have own weight class setting to indicate delivery API in what units package will be sent.