You apparently want to use drops to measure volume for a titration, for some OEM application. OK, but ... that doesn't depend just on the concentration of the liquid in the bottle. You also have to consider the fluid dynamics of the bottle -- how much it holds, how big the hole is, how hard will people squeeze, how the surface tension of the fluid will hold the liquid together until the drop breaks free. There's nothing terrible with the "drops" method of titration to an endpoint, but the answer will never be as accurate or precise as using real volumes measures using analytical glassware. The best you can do is try it multiple times and see how close you can get, compared to doing it analytically.