The pycnometer method is a precise laboratory technique used to measure the specific gravity (also known as relative density) of solids, liquids, or powders. Specific gravity is defined as the ratio of the density of the substance to the density of water at a specified temperature (typically 4°C or room temperature, around 20–27°C). A pycnometer, also called a specific gravity bottle, is a flask with a ground-glass stopper that has a small capillary hole, allowing it to hold a known, precise volume of liquid or material. This method is widely used in fields like soil mechanics, chemical engineering, and materials.