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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:

  • Supporting the equivalence of humidity measurements in the U.S. and abroad, through calibrations, standardized methods, and comparisons and proficiency testing
  • Providing customers access to the highest quality of humidity reference standards, through calibrations and reference data
  • Developing improved humidity standards
  • Supporting accurate measurements of humidity for various applications, such as fuel cells.
  • Studying thermophysical properties of gas mixtures that include water


Hybrid humidity generator – 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...

High Dew-point generator – Peter Huang of the Sensor Science Division's Thermodynamic Metrology Group has devised a new humidity generator that enables dew-point measurements up to 98 °C...

Gravimetric hygrometer for verification of NIST humidity standards – 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 CO2 – 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...

Thermophysical properties of moist gases – To support humidity measurements needed for the efficient operation of fuel cells, we have calculated numerous thermophysical properties of water-gas mixtures at elevated pressures...

Lead Organizational Unit:


Peter Huang
301-975-2621 Telephone

Christopher Meyer
301-975-4825 Telephone

Gregory Scace
301-975-2626 Telephone

100 Bureau Drive, M/S 8363
Gaithersburg, MD 20899-8363