kelvin | |
---|---|
General information | |
Unit system | SI |
Unit of | temperature |
Symbol | K |
Named after | William Thomson, 1st Baron Kelvin |
2019 definition | kB ≝ 1.380649×10−23 J/K |
Conversions | |
x K in ... | ... corresponds to ... |
Celsius | (x − 273.15) °C |
Fahrenheit | (1.8 x − 459.67) °F |
Rankine | 1.8 x °Ra |
The kelvin, symbol K, is the base unit of measurement for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts from 0 K, the lowest possible temperature (absolute zero), then rises by exactly 1 K for each 1 °C.[1][2][3][4] The Kelvin scale was designed to be easily converted from the Celsius scale (symbol °C). 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 redefinition of the SI base units 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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