Kilogram

"kg" redirects here. For other uses, see KG.

kilogram
A series of 5, 2, 1, 0.5 and 0.2 kilogram weights, made of cast iron
General information
Unit systemSI
Unit ofmass
Symbolkg
Conversions
1 kg in ...... is equal to ...
   Avoirdupois   
   British Gravitational   ≈ 0.0685 slugs
   CGS units   1000 g
   Daltons   6.02214076×1026 Da

The kilogram (also spelled kilogramme[1]) is the base unit of mass in the International System of Units (SI), having the unit symbol kg.[1] 'Kilogram' means 'one thousand grams'[2] and is colloquially abbreviated to kilo.[3]

The kilogram is an SI base unit, defined ultimately in terms of three defining constants of the SI, namely a specific transition frequency of 133Cs, the speed of light, and the Planck constant.[4]: 131  A properly equipped metrology laboratory can calibrate a mass measurement instrument such as a Kibble balance as a primary standard for the kilogram mass.[5]

The kilogram was originally defined in 1795 during the French Revolution as the mass of one litre of water. The current definition of a kilogram agrees with this original definition to within 30 parts per million. In 1799, the platinum Kilogramme des Archives replaced it as the standard of mass. In 1889, a cylinder composed of platinum–iridium, the International Prototype of the Kilogram (IPK), became the standard of the unit of mass for the metric system and remained so for 130 years, before the current standard was adopted in 2019.[6]


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  1. ^ a b Cite error: The named reference :1 was invoked but never defined (see the help page).
  2. ^ "Kilogram". Collins Online Dictionary. Retrieved 14 October 2024.
  3. ^ Merriam-Mebster definition of Kilo
  4. ^ Cite error: The named reference SIBrochure9thEd was invoked but never defined (see the help page).
  5. ^ "Mise en pratique for the definition of the kilogram in the SI". BIPM.org. 7 July 2021. Retrieved 18 February 2022.
  6. ^ Cite error: The named reference vox was invoked but never defined (see the help page).