New Definition of the Kilogram Based on the Planck Constant

Abstract

The kilogram had been the last SI base unit defined by the material artifact. In November 2018, it was adopted to revise the definition by using a defined number of the Planck constant. The new definition came into force on May 20th, 2019, the World Metrology Day. This historical change in the definition of the mass unit was realized by the progress of recent measurement technologies in the Kibble balance and the X-ray crystal density methods. A review is given on these methods, as well as what would be expected by the new definition of the kilogram.