Scientists have approved new hyper-accurate definitions for units of weight, electricity and temperature, bringing them into force starting May 20.
The introduced changes include "Le Grand K", the 130-year-old metal cylinder used to define what a kilogram is, which has now been retired in favour of a more precise measurement taken from a quantum ratio.
"The kilogram is the last unit of measurement based on a physical object," Thomas Grenon, director of France's National Laboratory of Metrology and Testing, said after the decision last year.
"The problem is that it's had a life, it could fluctuate. That's not good enough, given the level of precision we need today,” he added.
The kilogram will now be defined in terms of the Planck constant: the ratio of a frequency of light, on the one hand, to the quantum energy of that frequency, on the other (6.626 x 10-34 joule seconds).
Taking into consideration Einstein's equation according to which energy is linked to mass, the Planck constant can therefore be used to calculate mass based on the equivalent mechanical power needed to displace it.