Redefinition of the kilogram based on Planck's Constant

The theme for World Metrology Day 2018 is "Constant evolution of the International System of Units." In this brief, 2 1/2-minute video, Fluke Chief Corporate Metrologist Jeff Gust, explains why this year is so special to the science of measurements as it is anticipated that the definition of the kilogram will change from a metal artifact to Planck's Constant.

Video Transcript:

I'm Jeff Gust, chief corporate metrologist for Fluke Corporation. I'm here to talk about the redefinition of the kilogram as part of the celebration for World Metrology Day 2018. The theme this year is the constant evolution of the International System of Units.

The kilogram is part of the International System of Units or SI which is the modern form of the metric system. The SI represents the base units of measurement. This year something new and important is going to happen to the SI. Everything that you thought that you knew about the kilogram will change.

The kilogram was originally defined as the mass of 1 liter of water at 4 degrees Celsius, the point at which water is the most dense. It was replaced by a platinum cylinder artifact in the late 18th century. The International prototype kilogram or Le Grand K has been the world standard of math since 1889. It is stored in a locked vault near Paris, France. Opening the vault requires three keys from different parts of the world. At the last weigh-in, Le Grand K had lost about 50 micrograms which is roughly the weight of a single grain of sand. This is a problem because if the value of the kilogram changes, it influences every other measurement of mass in the world which results in trillions of dollars in trade differences.

We need to find a definition of the kilogram based on an unchanging constant of nature, and, while it's not been officially decided yet, we anticipate that later this year the kilogram will be based on a constant of nature - Planck's Constant. This fall, a draft resolution on the revision of the International System of Units will be submitted to the General Conference on Weights and Measures at its 26th meeting.

I'm excited about the upcoming change to the kilogram and the advancements in measurement science that have happened and are continuing to happen in our lifetime.

Fluke builds the world's most accurate, commercially-available standards for electrical, temperature, pressure, and flow measurement. Fluke's instruments are routinely used by the world's best scientists as part of the evolution of our system of measurement. This wouldn't be possible without the tireless efforts and valuable contributions of every employee within our company. So, on behalf of Fluke Corporation, happy World Metrology Day!

Additional Reading:

Learn more about the International System of Units at our "About Calibration" page.