for some reason, the droppers do vary. the best way to KNOW is to count the number of drops in one ml using an oral syrince as a graduated cylinder. those who were never afforded a middle school physics class, my sympathies.
using my SSKI , for example, there is one gram of KI per ml. count the number of drops it takes to give exactly one ml(8th grade physics) and divide that number into 1000mg and you have your number for that solution using that dropper in the manner that you like to use it. bingo bango.