Convert Pound (lb) to Kilogram (kg) instantly.
About these units
Pound (lb)
The pound is a traditional unit of mass widely used in the United States and, to a lesser extent, in the United Kingdom. Defined as exactly 0.45359237 kilograms, the pound evolved from medieval English systems that themselves descended from Roman and Carolingian traditions. The pound is central to commerce, engineering, food measurement, and body weight scales in the US. Its widespread cultural presence makes it deeply familiar even in contexts where metric units dominate. Because the pound is part of a non-decimal system, subdivisions such as ounces (1/16 pound) introduce complexity, yet this structure persists due to tradition and embedded industrial standards. In engineering, the pound often appears alongside pound-force, making careful distinction between mass and force essential.
Kilogram (kg)
The kilogram is the base unit of mass in the SI system and the only SI unit defined directly by a fundamental constant rather than a physical object. Originally, its definition was tied to a platinum–iridium artifact stored in France—the famous "International Prototype Kilogram." Over time, tiny mass changes in the prototype and its official copies created difficulties for high-precision science. In 2019, the kilogram was redefined using Planck's constant, linking mass to the laws of quantum physics through the Kibble balance. This innovation ensures universality, stability, and reproducibility across the world. The kilogram is central to commerce, science, engineering, and every quantitative field dealing with matter. Its decimal relationships with other metric units (grams, milligrams, tons) make it universally convenient. From groceries to spacecraft mass budgets, the kilogram anchors modern mass measurement.