A drop of water is equal to 0.050 milliliters. The unit used to represent a drop of water is 1 gtt metric.
This means that a drop of water, or 1 gtt metric, is equal to 1/20 of a milliliter. However, this is somewhat of an approximation as various factors can influence the exact volume of a drop of water. First of all, it depends where the drop of water is coming from. If it is being created by a standard dropper, then other factors also remain, such as the rate at which the drop was extracted and the resulting size of the drop. These factors actually become very significant with liquids different from regular water as their varying viscosity, surface tensions and densities could greatly affect the resulting volume of their drops.