Hydrometry or hydrometry is the science of measuring water and its related issues. In other words, hydrometry is the knowledge of examining the components of the hydrological cycle, including precipitation, underground water characteristics, as well as water quality and surface water flow characteristics.

Hydrometer, also known as hydrometer and hydrometer, is a device that can be used to measure the relative density of different fluids.

Because the commercial value of many liquids (such as sugar solutions, syrups, sulfuric acid, etc.) directly depends on their specific gravity, hydrometers are widely used in various industries.