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📚 Library of psychrometric functions to calculate 🌡️ thermodynamic properties of air for Python, C, C#, Fortran, R, JavaScript and VBA/Excel


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PsychroLib is a software library to enable the calculation of psychrometric properties of moist and dry air. Versions of PsychroLib are available for Python, C, C#, Fortran, R, JavaScript, Microsoft Excel Visual Basic for Applications (VBA). PsychroLib works in both metric (SI) and imperial (IP) systems of units. For a general overview and a list of currently available functions, please see the overview page.


Please see the Python API documentation for the common API across all the supported language implementations. In Python, array support and improved runtime performance can be optionally enabled by installing Numba. In R (1) constants, like ZERO_FAHRENHEIT_AS_RANKINE are not exported (i.e. not directly accessible to users), (2) functions accept a vector, not a scalar (3) bulk calculations, like CalcPsychrometricsFromRelHum return a list.

Examples on how to use PsychroLib in all the supported languages are described in this guide.


How to cite

When using PsychroLib, please cite the software summary paper and software version using the following Digital Object Identifiers (DOIs) to generate citations in your preferred style:

Software summary paper Software version*

*please make sure to cite the same version you are using with the correct DOI. For a list of all available versions see see more on Zenodo.


If you are looking to contribute, please read our Contributors' guide for details.


If you would like to know more about specific development guidelines and testing, please refer to our development notes.

Copyright and license

Copyright 2018-2020 The PsychroLib Contributors for the current library implementation.

Copyright 2017 ASHRAE Handbook — Fundamentals ( for equations and coefficients published ASHRAE Handbook — Fundamentals Chapter 1.

Software licensed under the MIT License.


Special thanks to:

For the full list of contributors, please see the contributors page.