International Temperature Scale of 1990

<p>The International Temperature Scale of 1990 (ITS-90) is an equipment calibration standard specified by the <a href="/facts/CIPM/a1FPjTtr">International Committee of Weights and Measures</a> (CIPM) for making measurements on the <a href="/facts/Kelvin/E3trzC4C">Kelvin</a> and <a href="/facts/Degree_Celsius/okAEu1CA">Celsius</a> <a href="/facts/Temperature_scale/b2D6632R">temperature scales</a>. It is an approximation of thermodynamic temperature that facilitates the comparability and compatibility of temperature measurements internationally.  
It defines fourteen calibration points ranging from 0.65 K to 1357.77 K (−272.50 °C to 1084.62 °C) 
and is subdivided into multiple temperature ranges which overlap in some instances.
ITS-90 is the most recent of a series of International Temperature Scales adopted by the CIPM since 1927.
Adopted at the 1989 General Conference on Weights and Measures, it supersedes the International Practical Temperature Scale of 1968 (amended edition of 1975) and the 1976 "Provisional 0.5 K to 30 K Temperature Scale". The CCT has also published several online guidebooks to aid realisations of the ITS-90.
The lowest temperature covered by the ITS-90 is 0.65 K. In 2000, the temperature scale was extended further, to 0.9 mK, by the adoption of a supplemental scale, known as the <a href="/facts/Provisional_Low_Temperature_Scale_of_2000/Njtpjzfs">Provisional Low Temperature Scale of 2000</a> (PLTS-2000).
</p><p><a href="/facts/2019_revision_of_the_SI/g0h07jCX">In 2019, the kelvin was redefined</a>. However, the alteration was very slight compared to the ITS-90 uncertainties, and so the ITS-90 remains the recommended practical temperature scale without any significant changes. It is anticipated that the redefinition, combined with improvements in primary thermometry methods, will phase out reliance on the ITS-90 and the PLTS-2000 in the future.
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International Temperature Scale of 1990 open-in-new

International Temperature Scale of 1990