Kelvin

The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. It is defined by two facts: zero kelvin is absolute zero (when molecular motion stops), and one kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water (0.01°C). The Celsius temperature scale is now defined in terms of the kelvin.

The kelvin is named after the physicist and engineer William Thomson, who became Lord Kelvin when he was made a peer.

The kelvin as an SI unit is correctly written with a lowercase k (unless at the beginning of a sentence), and is never preceded by the words degree or degrees, or the symbol °, unlike Fahrenheit, or Celsius. This is because the latter are scales of measurement, whereas the kelvin is a unit of measurement. When the kelvin was introduced in 1954 (10th CGPM, Resolution 3, CR 79), it was the "degree Kelvin", and written °K; the "degree" was dropped in 1967 (13th CGPM, Resolution 3, CR 104).

Note that the symbol for the kelvin unit is always a capital K and never italicised.

Conversion factors

In a thermodynamic system, the energy carried by the particles is proportional to the absolute temperature, where the constant of proportionality is the Boltzmann constant. As a result, it is possible to determine the temperature of particles with a certain energy; or to calculate the energy of particles at a certain temperature:

electron volts to kelvin

• Temperature Conversions: Celsius (Centigrade), Fahrenheit, Kelvin, Réaumur, and Rankine
• Conversion calculator for units of temperature