Convert Stone (st) to Kilogram (kg) instantly.
About these units
Stone (st)
The stone equals 14 pounds, or approximately 6.35029 kilograms, and is commonly used in the United Kingdom and Ireland for expressing human body weight. It has deep traditional roots, originating from stones used as counterweights in early commerce. Although largely replaced by metric units in most applications, the stone remains emotionally and culturally significant for personal weight expression in the UK. Many people find it more intuitive and relatable than kilograms due to long-standing social habits. The stone's endurance highlights how measurement systems reflect cultural identity as much as mathematical convenience. It is one of the few units still commonly used in conversation but not in scientific or industrial contexts.
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.