# Kelvin

## SI unit of temperature / From Wikipedia, the free encyclopedia

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The **kelvin**, symbol **K**, is a unit of measurement for temperature.[1] The **Kelvin scale** is an absolute scale, which is defined such that 0 K is absolute zero and a change of thermodynamic temperature T by 1 kelvin corresponds to a change of thermal energy *kT* by 1.380649×10^{−23} J. The Boltzmann constant *k* = 1.380649×10^{−23} J⋅K^{−1} was exactly defined in the 2019 redefinition of the SI base units such that the triple point of water is 273.16±0.0001 K.[2] The kelvin is the base unit of temperature in the International System of Units (SI), used alongside its prefixed forms.[2][3][4] It is named after the Belfast-born and University of Glasgow-based engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907).[5]

**Quick facts: kelvin, General information, Unit system, Uni...**▼

kelvin | |
---|---|

General information | |

Unit system | SI |

Unit of | temperature |

Symbol | K |

Named after | William Thomson, 1st Baron Kelvin |

Conversions | |

x K in ... | ... corresponds to ... |

Celsius | (x − 273.15) °C |

Fahrenheit | (1.8 x − 459.67) °F |

Rankine | 1.8 x °Ra |

Historically, the Kelvin scale was developed from the Celsius scale, such that 273.15 K was 0 °C (the approximate melting point of ice) and a change of one kelvin was exactly equal to a change of one degree Celsius.[1][5] This relationship remains accurate, but the Celsius, Fahrenheit, and Rankine scales are now defined in terms of the Kelvin scale.[2][6][7] The kelvin is the primary unit of temperature for engineering and the physical sciences, while in most countries the Celsius scale remains the dominant scale outside of these fields.[5] In the United States, outside of the physical sciences, the Fahrenheit scale predominates, with the kelvin or Rankine scale employed for absolute temperature.[6]

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