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The NIST Thermodynamic Metrology Group maintains and develops national standards of humidity (in the range 1 nmol/mol to 0.6 mol/mol of water concentration), and supports calibration of all types of hygrometers and humidity generators. It also engages in research to improve humidity standards and study thermophysical properties of moist gases.


Our goals include:

  • Providing SI traceability of humidity standards through use of standardized realization methods, and supporting humidity measurements in the U.S. and abroad through calibrations and proficiency testing
  • Ensuring the equivalence of US humidity standards with those of other countries though participation in international comparisons 
  • Providing customers access to the highest quality of humidity reference standards, through calibrations and reference data
  • Developing improved humidity standards
  • Supporting accurate knowledge of humidity properties for various industrial applications, such as Carbon Capture and Sequestration.
  • Studying thermophysical properties of gas mixtures that include water

Humidity Calibration Services at NIST – NIST's new primary standard humidity generator, the Hybrid Humidity Generator (HHG), replaces the NIST 2-Pressure Humidity Generator, Mark 2 (2-P). The HHG produces humidified air...

NIST Gravimetric Hygrometer for Verification of NIST Humidity Standards and for Research on Humidity Properties – The NIST Thermometry Group recently christened a second generation gravimetric hygrometer, and a description of the hygrometer was published in Metrologia...

Dew-point measurements for water in compressed gases – The NIST Thermodynamic Metrology Group (TMG) is using its standard gravimetric hygrometer as part of a facility for making high-accuracy measurements of the dew point temperature for water in compressed CO2 as a function of mole fraction and pressure...

Dynamic Humidity Measurements with the Hybrid Humidity Generator –The HHG and its accompanying temperature-controlled test chamber may also be used as a research tool for performing studies involving rapid changes in humidity...

Created September 26, 2011, Updated May 11, 2021