Unit Converters

History

The kilogram was originally defined in 1799 as the mass of one liter of water at 4°C. For over a century, it was defined by a physical platinum-iridium cylinder kept in Paris. In 2019, the kilogram was redefined in terms of the Planck constant, making it the last SI base unit to be defined by a fundamental physical constant rather than a physical artifact.

History

The pound has ancient origins, deriving from the Roman 'libra pondo' (hence the abbreviation 'lb'). The modern avoirdupois pound was standardized in 1959 by international agreement at exactly 0.45359237 kilograms. It has been a fundamental unit of trade and commerce for centuries.