Kilograms vs Pounds

Both units are now defined against the same standard, which is the part most people do not realise. The international yard and pound agreement of 1959 pinned the pound to exactly 0.45359237 kilograms, so the pound is not an independent unit at all — it is a defined fraction of the kilogram. The kilogram itself was redefined in 2019 in terms of the Planck constant, retiring the platinum-iridium cylinder held near Paris that had served as the physical standard since 1889. That change rippled through to the pound automatically. In practice one kilogram is 2.204623 pounds, so a 70 kg person weighs 154.3 lb. The pound survives in everyday use in the United States and, informally, in the United Kingdom, where body weight is still commonly given in stones and pounds while food is sold in metric. Almost everywhere else, and in every laboratory, the kilogram is used exclusively.