The primary unit of mass in the metric system is the kilogram. It is widely used around the world for scientific, commercial, and everyday measurements. One kilogram is defined as being equal to the mass of the International Prototype of the Kilogram, a platinum-iridium cylinder stored in France. The kilogram is the base unit of mass in the International System of Units (SI) and serves as a fundamental reference for measuring mass, weight, and density in various fields, including engineering, physics, and nutrition. Its widespread adoption has facilitated standardization in global commerce and science.