Kilogram (kg)

• Definition: The SI base unit of mass. Since 2019, it has been defined in terms of the Planck constant, securing a completely stable physical value.
• History: Originally defined in 1795 in France as the mass of one liter of pure water at the freezing point. For over a century, it was defined by a physical platinum-iridium cylinder stored in France.
• Common Uses: The universal standard for measuring human body mass, commercial freight weights, and grocery items globally.

Pound (lbs)

• Definition: A unit of mass/weight used in the US Customary and Imperial systems, defined since 1959 as exactly 0.45359237 kilograms (specifically the avoirdupois pound).
• History: Descended from the Roman libra (hence the abbreviation “lbs”). England standardized various regional versions of the pound in the 14th century.
• Common Uses: Measuring body weight, grocery shopping items, and shipping weights in the US.