Title: relative humidity
Long Title: IUPAC Gold Book - relative humidity
DOI: 10.1351/goldbook.R05267
Status: current

Definition
The ratio, often expressed as a percentage, of the partial pressure of water in the atmosphere at some observed temperature, to the saturation vapour pressure of pure water at this temperature.

Related Terms
- partial pressure: https://goldbook.iupac.org//terms/view/P04420
- saturation vapour pressure: https://goldbook.iupac.org//terms/view/S05479

Source
- PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2210 (https://doi.org/10.1351/pac199062112167)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/R05267/html
- json: https://goldbook.iupac.org/terms/view/R05267/json
- xml: https://goldbook.iupac.org/terms/view/R05267/xml

Citation: Citation: 'relative humidity' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.R05267
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-05-06T22:25:49+00:00