Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Fluid Metrology Group

Develops models, standards, reference data, methods, and uncertainty analyses for metering liquid and gas flows, airspeed, liquid density, and volume. We measure micro-flows (e.g., pharmaceuticals) and mega-flows (e.g., natural gas in major pipelines, pollutants from power plants).

The Fluid Metrology Group maintains the national standards for flow quantities, including gas and liquid flow, airspeed, liquid volume, and liquid density. For instance, the group maintains six flow calibration systems to measure gas flows from 0.1 cm3/min to 105 m3/min (an eleven decade flow range) and five primary liquid flow standards to cover five decades of flow range. The group’s unique and often best in the world facilities are used to conduct collaborative research on flow measurement, to perform calibrations of reference meters that meter manufacturers use to calibrate their products, and to perform proficiency tests for commercial laboratories seeking accreditation. 

NIST flow measurements contribute to nearly every US economic sector including defense, energy, transportation, pollution control, and the manufacture of pharmaceuticals and semi-conductors. The group’s volume and gas flow standards ensure equitable trade of trillions of dollars' worth of petroleum and natural gas each year. Our research is focused on improving primary standards that realize flow units and improving the physical models of flow meters so that their calibrations can be extrapolated to real applications with the required accuracy. The group works closely with leading US meter manufacturers and users, government agencies, and academic research institutes to provide new measurement solutions for emerging needs. We participate in national and international documentary standards efforts that ensure product quality and advance US trade. 


  • Documentary Standards
    The group’s staff are active in the development of Documentary Standards on various Standards Developing Organizations (SDOs) by providing the necessary expertise, fundamental measurement science, and testing. We engage with the following SDOs: ASME, ASTM, API, and ISO.


The Fluid Metrology Group welcomes opportunities to collaborate on joint research, technology, and standards development projects to advance flow metrology. The group provides multiple opportunities for students, scientists, industry, academia, and other R&D laboratories to collaborate. Specific opportunities depend on current areas of interest within the group, but may include undergraduate research fellowships, postdoctoral fellowships, visiting scientists, and guest researchers as well as various cooperative research arrangements ranging from formal agreements, such as CRADAs, Consortia, and interagency agreements, to informal collaborations. For more details, see Employment and Internship Opportunities and Collaboration Opportunities.

Projects and Programs

Acoustic Techniques in Fluid Metrology

The Fluid Metrology Group leads the world in designing and using gas-filled acoustic resonators for measuring the thermodynamic temperature T, the Boltzmann

Air Speed Metrology

NIST's versatile wind tunnel is used to calibrate customers' airspeed sensors and to conduct research on the design of novel anemometers, the responses of

Atomic Standard for Pressure

NIST scientists are developing a highly accurate primary standard for pressure in the range 2 MPa to 7 MPa based on fundamental physical properties of helium

Tools and Instruments

Transient Gas Flow Facility

A compressor is used to pressurize up to twenty-five 40 L gas cylinders to 35 MPa. The cylinders can then be used as a source of rapidly changing gas flow by

Gas Flow Standards

NIST uses pressure, volume, temperature, and time ( PVTt) standards to calibrate gas flow meters. PVTt flow standards generate selected, steady gas flows

Wind Tunnel

NIST’s wind tunnel can produce air speeds between 0.15 m/s and 40 m/s. The air speed reference is a Laser Doppler Anemometer (LDA) with an uncertainty of 2.5 %

News and Updates

Sounding Out a New Way to Measure Gas Flow

Researchers at NIST have developed a new — and sound — way to accurately measure the rate at which gas flows in and out of a vessel. The technique, which uses

Reliable Flow for Chip Makers

Researchers at the National Institute of Standards and Technology (NIST) have begun an ambitious project to attack a vexing problem in the semiconductor


Non-nulling Protocols for Fast, Accurate, 3-D Velocity Measurements in Stacks

Iosif Isaakovich Shinder, Aaron Johnson, James Filla, Vladimir B. Khromchenko, Michael R. Moldover, Joey Boyd, John D. Wright, John R. Stoup
We present protocols for making fast, accurate, 3-D velocity measurements in the stacks of coal-fired power plants. The measurements are traceable to

Gas Flow Standards and Their Uncertainty

John D. Wright, Aaron Johnson, Michael R. Moldover, Shin-ichi Nakao
We review diverse types of gas flow standards that are used to calibrate other gas flow meters. For each type of standard, we describe the principles of its

Evaluating Inter-Laboratory Comparison Data

Enrico Frahm, John D. Wright
The primary purpose of inter-laboratory comparisons is to demonstrate that the uncertainty specifications of the calibration measurement capabilities of the



Office Manager