India adopts new standard definition of Kg, kelvin, mole and ampere

The definition of the base units has been changed from being linked to artefacts to being based on the fundamental constants on nature.

May 22, 2019 11:20 IST
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India on May 20, 2019 joined several nations across the world in implementing the new definition of four of the seven base units - kilogramme, kelvin, mole and ampere. With this, the definition of the base units will change in the national records, including in the textbooks.

The resolution to redefine four of the seven base units was passed by representatives of 60 countries including India at the 26th meeting of the General Conference on Weights and Measures (CGPM), which was held from November 13-16, 2018 in Versailles, France.  The resolution was scheduled to come into force on May 20, 2019.


The CGPM is the highest international body of the world for accurate and precise measurements. It comprises 60 countries and 42 Associate Members.

India was represented at the meeting by Consumer Affairs Secretary Avinash K Srivastava, National Physical Laboratory (NPL) Director D K Aswal and Head of NPL’s Planning, Monitoring & Evaluation TD Senguttuvan.

Key Highlights

The definition of the base units, also known as the International System of Units (SI), has been changed from being linked to artefacts to being based on the fundamental constants on nature.

Overall, the definition of seven base units including second, metre, kilogram, ampere, Kelvin, mole and candela has been changed.

The key aim behind redefining the system units is to enable worldwide coherence of measurements.

The new change in the definitions will result in uniform and worldwide accessible SI system for international trade, high- technology manufacturing, human health and safety, protection of the environment, global climate studies and the basic science underpinning these.

The International System of Units (SI) was established in 1960 and has been updated several times to account for development in measurement technology.


The unit redefinitions represent a profound change of perspective and they are expected to form the foundations of improved measurements for decades to come as science and technology continues to develop in ways scientists cannot currently foresee.

However, the proposed changes have been designed to have no immediate consequences. However, they will matter when it comes to measurements less than a kilogramme for instance, while measuring smaller diamonds.


The International Bureau of Weights and Measures (BIPM), the main executive body of CGPM has the responsibility of defining the International System of Units (SI).

NPL has sent recommendations to the National Council of Educational Research and Training (NCERT) to implement the proposed changes in contemporary education.

Besides this, recommendations have been sent to the All India Council for Technical Education (AICTE), Indian Institutes of Technology (IITs), National Institutes of Technology (NITs) and other academic institutes to incorporate the proposed changes in the syllabus of metrology courses in graduate engineering and academic courses.

26th General Conference on Weights and Measures redefines standard definition of Kg

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