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10/26/2026 | Press release | Archived content

Conversion of Reported Temperatures from Historical Scales to the ITS-90

Published
October 26, 2026

Author(s)

Allan Harvey

Abstract

While the International Temperature Scale of 1990 (ITS-90) has been a standard for many years, there is a large amount of historical thermophysical data reported on other scales. The differences of these scales from ITS-90 is typically small, but not necessarily negligible for reference-quality work. We describe conversion to ITS-90 from 34 different scales. These include not only the relatively well-known International Temperature Scales from 1968, 1948, and 1927, but also scales that have been used for cryogenic work at temperatures below the ranges of the older international scales, including the many scales that were based on the vapor pressure of helium. Scales specific to certain laboratories are also considered. Python code has been made available for the conversions described here.
Citation
International Journal of Thermophysics
Volume
47
Issue
11
Pub Type
Journals

Keywords

metrology, temperature, thermophysical properties

Citation

Harvey, A. (2026), Conversion of Reported Temperatures from Historical Scales to the ITS-90, International Journal of Thermophysics, [online], https://doi.org/10.1007/s10765-026-03849-w, https://nps-ext.nist.gov/nps/nps_public_api/api/Publication/file/962313 (Accessed October 28, 2026)
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NIST - National Institute of Standards and Technology published this content on October 26, 2026, and is solely responsible for the information contained herein. Distributed via Public Technologies (PUBT), unedited and unaltered, on October 28, 2026 at 09:14 UTC. If you believe the information included in the content is inaccurate or outdated and requires editing or removal, please contact us at [email protected]