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World Metrology Day

20 May 2019

A landmark day for the metrology community and NPL

The 20 May 2019 is the first day of the redefined International System of Units (SI). This change has been eagerly awaited by the entire international metrology community and represents one of the most significant changes to the SI since its creation.

From 20 May, definitions of four units (the kilogram, the ampere, the kelvin and the mole) will be revised. This means that the definitions of all the SI units will be linked to constants of nature, not physical artefacts. This will guarantee their stability and universality.

Over the past 30 years, NPL has been at the forefront of the international, collaborative research that comes to fruition today.

If you have press enquiries, questions on the science or want to know about NPL's activities, then please contact us.

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The redefinition will pave the way for more precise measurement and accurate science

Find out more about the SI units that are being redefined from the lead researchers in each area.

     

     

Read more about the SI units

Changes in the International System of Units of measurement

Fiona Auty, Head of Government Relations and Corporate Communications at NPL

Read blog

The redefinition of the SI

Find out the impact of the SI redefinition and how it will affect your calibration services

The redefinition of the SI

Science loses a kilogram

On 20 May 2019, World Metrology Day, the world says goodbye to the original kilogram as the redefinition of the SI base units come into force.

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Supporting science learning in schools

To celebrate and explain the SI definitions, NPL has published 12 new schools posters describing the SI and measurement.

School posters

BIPM on the revision of the SI

In a landmark decision, the BIPM's Member States voted on 16 November 2018 to revise the International System of Units (SI), changing the world's definition of the kilogram, the ampere, the kelvin and the mole. The decision, made at the 26th meeting of the General Conference on Weights and Measures (CGPM) in Versailles, France, means that all SI units will now be defined in terms of constants that describe the natural world.

The new definitions will come into force on 20 May 2019, World Metrology Day.

Find out more from BIPM

Read more on World Metrology Day and download the official poster

Celebrate the redefinition of the SI with NPL

Join us as we take over the Lates to mark the historic redefinition of the SI

Science Museum | London
29 May 2019