Units of Measurement of Kilogram,Kelvin,Mole and Ampere Redefined (Download PDF)


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Representatives from 60 countries voted to redefine the International System of Units (SI), changing the world’s definition of the kilogram, the ampere, the kelvin and the mole. The decision was made at the General Conference on Weights and Measures in Versailles, France, which is organised by the International Bureau of Weights and Measures (BIPM).

This is image show in measurement of Kilogram,Kelvin,Mole

This is Image Show in Measurement of Kilogram, Kelvin, Mole

This is image show in measurement of Kilogram, Kelvin, Mole


  • From 20th May 2019 (World Metrology Day) itself this change will be implemented where the SI units will now be defined in terms of constants describing the natural world.

  • This would also bring an end to the use of physical objects to define measurement units.

  • It will be replaced by the Planck constant -the fundamental constant of quantum physics.

  • The stability of the IPK could only be confirmed by comparisons with identical copies, a difficult and potentially inaccurate process, the Planck constant is ready for use everywhere and always.

  • The new definitions impact four of the seven base units of the SI: the kilogram, ampere, kelvin and mole; and all units derived from them, such as the volt, ohm and joule.

  • The kilogram -will be defined by the Planck constant (h)

  • The ampere -will be defined by the elementary electrical charge (e)

  • The kelvin -will be defined by the Boltzmann constant (k)

  • The mole -will be defined by the Avogadro constant (NA)

  • The size of these units will not change (a kilogram will still be a kilogram), the four redefined units will join the second, the metre and the candela to ensure that the set of SI base units will continue to be both stable and useful.

  • The revised SI will maintain its relevance by facilitating technical innovations. The new changes will have wide-reaching impact in science, technology, trade, health and the environment, among many other sectors.

Latest Updates

  • Quantum computing, artificial intelligence (AI), Industry 4.0, space enabled communications, are some of the international challenges of the near future.

  • As a national responsibility and keeping in view of the importance and recognition of new revision of SI, the CSIR-NPL has also prepared documents on:

    • NPL Policy on Metrological Traceability,

    • Recommendations on the proposed changes to be incorporated in the National Council of Educational Research and Training (NCERT), New Delhi textbooks and implement the new changes to impart cotemporary education to its students and

    • Recommendations on the proposed changes to be incorporated in syllabi of metrology courses in graduate engineering and academic courses being taught in All India Council for Technical Education (AICTE), Indian Institutes of Technology (IITs), National Institutes of Technology (NITs), and other academic institutes.

  • A book entitled, “Redefined SI Units and Glimpses of NPL Metrological Activities” of almost 100 pages to percolate and disseminate the information accommodating details on new changes was also published on this occasion by CSIR-NPL.

  • Posters and documents mentioned above and role of NPL in strengthening the Indian metrological infrastructure for the govt. representatives, policy makers, regulator, certification bodies, academic institutions, industries and public as a whole.

- Published/Last Modified on: August 3, 2019


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