Special Issue: Today's Official Launch of the Redefined International System of Units

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A biweekly news digest from the
National Institute of Standards and Technology

MAY 20, 2019

A hand holds up a card describing the constants.

A Turning Point for Humanity: Redefining the World’s Measurement System

Today—World Metrology Day 2019—is the official launch date of the newly redefined International System of Units (SI). This special issue of Tech Beat brings together some of our past and present content on the SI redefinition. To start things off, here is our introductory essay on the revised SI.


NIST delegation to SI vote.

Historic Vote Ties Kilogram and Other Units to Natural Constants

On November 16, 2018, a group of 60 nations voted to implement the most significant change to the International System of Units (SI) in more than 130 years.


NIST cold core technology

For All Times, For All Peoples: How Replacing the Kilogram Empowers Industry

Jim Olthoff, NIST's associate director of laboratory programs, explains how redefining the kilogram will empower industry.


Five scientists celebrating at SI redefinition vote.

The ‘Gang of Five’ and the SI Revolution

In this new blog post, NIST's Peter Mohr recounts the backstory of the radical idea behind redefining the kilogram and the SI in general.


Paper napkin with lists of numbers written on it.

A Massive Bet: The Planck Napkin

A bunch of metrologists walk into a bar—and try to guess the value they will measure for the Planck constant. Who came closest?



Learn all about the seven base units of the SI—from the kilogram to the candela, in NIST's microsite on the revised SI!


more news and announcements

Meet the Constants

The revised SI rests on a foundation of seven values, known as the constants. Learn more in our quick tour of them. 

Reason and Measurement, Suits and Ties: My Personal Journey to the New SI

NIST physicist Jon Pratt reflects on his road to the revised SI and what it means for humankind.

Proving Our Mettle: NIST and the Boltzmann Constant Olympics

NIST's Michael Moldover describes the role he played in measuring the Boltzmann constant, one of the new cornerstones of the revised SI.

Video: Metric Makeover

Opening shot of metric video.

Just nominated for an EMMY award! See this NIST video, which has been broadcast worldwide and is available in seven languages. It explains the SI redefinition and its importance to our world. Also, explore other visual resources that you can share with your friends and colleagues!