Kelvin

This article is about the unit of temperature. For the person, see Lord Kelvin. For other uses, see Kelvin (disambiguation).

kelvin
Equivalent temperatures in kelvin (K), Celsius (°C), and Fahrenheit (°F)
General information
Unit systemSI
Unit oftemperature
SymbolK
Named afterWilliam Thomson, 1st Baron Kelvin
2019 definitionkB ≝ 1.380649×10−23 ⁠J/K⁠
Conversions
x K in ...... corresponds to ...
   SI derived units   (x − 273.15) °C
   Imperial/US units   (1.8x − 459.67) °F
   Imperial/US absolute scale   1.8x °Ra

The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K.[1][2][3][4] By definition, the Celsius scale (symbol °C) and the Kelvin scale have the exact same magnitude; that is, a rise of 1 K is equal to a rise of 1 °C and vice versa, and any temperature in degrees Celsius can be converted to kelvin by adding 273.15.[1][5]

The 19th century British scientist Lord Kelvin first developed and proposed the scale.[5] It was often called the "absolute Celsius" scale in the early 20th century.[6] The kelvin was formally added to the International System of Units in 1954, defining 273.16 K to be the triple point of water. The Celsius, Fahrenheit, and Rankine scales were redefined in terms of the Kelvin scale using this definition.[2][7][8] The 2019 revision of the SI now defines the kelvin in terms of energy by setting the Boltzmann constant to exactly 1.380649×10−23 joules per kelvin;[2] every 1 K change of thermodynamic temperature corresponds to a thermal energy change of exactly 1.380649×10−23 J.

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  2. ^ a b c Cite error: The named reference SI Brochure 9 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference BIPM web page for kelvin was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference NIST SI redefinition was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference nist intro was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference absoluteC was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Busting Myths about the Metric System was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference NIST HB44 Appendix C was invoked but never defined (see the help page).