Answer:
It depends on the eye dropper, to find out how much your specific eyedropper holds count the number of times it takes to empty a 100ml beaker using it. Divide the amount of water in the beaker by the number of times it took to empty it and you will have a rough approximation of how many mL your eye dropper will hold.
A standard small bottle with dropper - one suck which fills the dropper to about 2/3 of its height should be 1 ml.