Since consumption varies by user, the easiest way to measure your electrolyte intake is to divide the amount of electrolytes in one cartridge by the average number of bottles you are getting from a single cartridge.
Example, if you use a setting around 8-10 and get two bottles from one cartridge then you are consuming half the electrolytes in a cartridge per full bottle of water.
The "Dial Your Performance" chart can be used as a reference to help you get started.