The standard unit for measuring mass in the International System of Units (SI) is the kilogram, symbolized as kg. The kilogram is the base unit and is used in a wide array of scientific and engineering applications. It provides a consistent standard for measurement worldwide, facilitating communication and data comparison between different studies and disciplines. The historical definition of the kilogram was based on a physical object, the International Prototype of the Kilogram, but it is now defined by a constant, the Planck constant, ensuring precision.