|1 kg in ...||... is equal to ...|
| || ≈ 2.205|
|British Gravitational|| ≈ 0.0685|
The kilogram or kilogramme (symbol: kg) is the
The kilogram was originally defined as the mass of a litre (cubic decimetre) of water at its freezing point. That was an inconvenient quantity to precisely replicate, so in the late 18th century a platinum artefact was fashioned as a standard for the kilogram. That artefact, or an exact replica thereof, has been the standard of the unit of mass for the metric system ever since.
Though the IPK, the current primary artefact, and its replicas are stored in carefully controlled laboratory conditions, their masses have been subject to fluctuation as a result of poorly understood factors, possibly including handling, cleaning and contamination. The IPK has diverged from its replicas by 50 μg since their manufacture late in the 19th century. This has led to calls to replace the artefact with a standard defined in terms of invariant constants of nature.
The kilogram is the only named SI unit with an
The IPK is rarely used or handled. Copies of the IPK kept by
The International Prototype Kilogram was commissioned by the