Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Resources for Reporters

The following resources may be used by media outlets when reporting on the SI redefinition. Videos should be credited to NIST. Photos should include the appropriate credit.

Scientists Vote on Metric Makeover

After decades of groundbreaking laboratory work, the world’s scientific and technical community has redefined four of the seven base units for the International System of Units (SI). A vote to adopt the change took place on November 16, 2018, at Versailles, France. The affirmative vote means the kilogram (mass), kelvin (temperature), ampere (electric current) and mole (amount of substance) are now determined by fundamental constants of nature instead of by physical objects. This historic change is the largest single shift in international measurement since the Treaty of the Meter was signed in 1875. Scientists expect this change will spur technological innovation and lower the cost of many high-tech manufacturing processes.

In English. Watch this video on YouTube.

In French.

In Mandarin.

In Spanish.

In German.

In Portuguese.

The video above was produced by the National Institute of Standards and Technology.
Writer/Director: José Ricardo García · Producers: Leon Gerskovic, Robin Materese · Executive Producers: Kevin Kimball, Gail Porter · Scientific Adviser: Ben Stein · Animation by Fugu GFX ( · Director of Animation: Ariel Martian · Producer of Animation: Jodie Baltazar · Art Director/Illustrator/Animator: Ariel Martian · 3D Artist: Talon Nightshade · Animatics Editor: Jodie Baltazar · Illustrator: Songgu Kwon · Post Production Sound Services by Studio Unknown · Re-recording Mixer: Kevin Hill, CAS · Sound Designer/ Sound Effects Editor: Cazz Cerkez · Dialogue Editor: Kevin Hill · Audio Post Coordinator: Jaime Horrigan · Audio Post Office Manager/Voice Casting: Mandisa Henry · Original Music by: Cazz Cerkez

Additional Multimedia Materials

Watch this video on YouTube.


kilograms under glass jars
Credit: J.L. Lee/NIST
NIST's platinum-iridium kilogram K92 (front) with stainless-steel kilogram masses in the background.
NIST researcher Mike Moldover with a basketball-sized metal sphere used to measure the speed of sound in a gas
Credit: NIST
Michael Moldover and an acoustic resonator he and his colleagues developed for making some of the world's most accurate measurements of the Boltzmann constant. Read more about Mike's work in this blog post.
The NIST-4 watt balance
Credit: J. L. Lee / NIST
The NIST-4 watt balance has measured Planck's constant to within 34 parts per billion, demonstrating that the high-tech scale is accurate enough to assist with 2018's planned redefinition of the kilogram.
Man in clean suit and purple gloves holding a kilogram sample with tongs
Credit: J.L. Lee/NIST
NIST's Eddie Mulhern holding K92, one of the agency's kilogram masses.
Person holding wallet card showing the values of fundamental constants being used for revising the International System of Units, the modern metric system.
Credit: Stoughton/NIST
This wallet card displays the fundamental constants and other physical values that will define a revised international system of units.
gold chip
Credit: NIST
Single-electron transport (SET) chip that could be used to count electrons in a redefined ampere.

Outer circle has one wedge for each of the 7 SI units (kilogram, meter, second, ampere, kelvin, mole, and candela) and the inner circle has wedges for the 7 important constants.
Credit: BIPM
Download the image files for this logo.

Looking to interview someone from NIST about the SI Redefinition? Contact jennifer.huergo [at] (subject: SI%20Redefinition%20Interview%20Request) (Jennifer Huergo) (301-975-6343) or bstein [at] (subject: SI%20Redefinition%20Interview%20Request) (Ben Stein) (301-975-2763).

Created September 11, 2018, Updated June 12, 2019