A hydrometer is a precision instrument designed to measure the specific gravity (relative density) of liquids. Commonly used in industries such as food & beverage, chemical, petroleum, brewing, and laboratory testing, hydrometers provide an accurate indication of liquid concentration, purity, or strength.

Made from durable glass or high-quality plastic, a hydrometer typically consists of a weighted bulb at the bottom that allows it to float upright, and a calibrated stem for easy reading of measurements. Depending on its application, it can be used to measure alcohol content, sugar levels, battery acid strength, or salinity in water.