Glass droppers fill about 1 ml of liquid. That should fill the dropper about 1/2 way but may fill a little less due to the amount of air in the glass pipette.
Do not overtighten your droppers onto the bottle as it could potentially break the glass pipette. If you notice that your glass pipette is not screwing in straight, you can gently press the glass pipette into the rubber bulb to shorten the length of the glass pipette.
We do not sell graduation glass droppers. Our droppers do not have interval marks on them.