This converter requires the use of Javascript enabled and capable browsers. This script creates a weight converter that is ONLY valid for water weights and volumes. It allows for the crossing of boundaries between volume and weight. Enter the unit value for the conversion. Select what you wish to convert from and wish to convert to. The result will be displayed blow the tables. The weights are based on PURE water, or distilled water. A gallon of sea water (saltwater) will weight more than a gallon of freshwater because of the totally dissolved salts (TDS) in it. The density is greater; how much greater and how much heavier depends on the saturation.