Convert Stone (US) to Kilogram

The stone as a unit of mass has roots dating back to ancient times, where it was used in various cultures for weighing goods, with the weight of a stone varying by country and commodity. In the UK, the stone was historically used to measure items like wool, and the weight of the stone varied (ranging from 5 to 30 pounds) based on the goods being measured. The U.S. adopted a 14-pound stone in the 19th century, primarily as a way to measure body weight, though it is now largely replaced by the pound for more precise measurements. The 14-pound stone is still used informally in some areas, especially in the context of body weight.

The kilogram originated during the French Revolution in the late 18th century as part of the metric system's development. Initially, it was defined as the mass of one cubic decimeter of pure water at 4°C, chosen for its universal availability and consistency. In 1799, a physical standard called the Kilogram of the Archives, a platinum cylinder, was created to represent the unit. Later, in 1889, the International Prototype of the Kilogram (IPK), a more precise platinum-iridium cylinder, was adopted as the global standard, stored in France with copies distributed worldwide.

Over time, physical changes in the IPK led to inconsistencies, prompting scientists to redefine the kilogram. In 2019, it was redefined based on the Planck constant (h), a fundamental constant of nature, linking the kilogram to unchanging physical properties rather than a physical object. This modern definition ensures long-term precision and stability for the unit of mass.