The Latin letter [U:004B] is used to indicate heating or cooling on the Kelvin scale. Note that the degree symbol [U:00B0] is not used before this letter. Such a notation was established at the General Conference on Weights and Measures in 1967.

Kelvin is one of the main units of temperature measurement. The scale is based on Boltzmann's constant, and its zero coincides with absolute zero – the minimum temperature limit in the universe.

The symbol "Kelvin degree sign" may be used in any texts about climate and weather, on websites with hydrometeorological forecasts, and in scientific works on chemistry and physics.