Definition of kilogram changed after 130 years

The changes, which will come into force on May 20 next year, will bring an end to the use of physical objects to define measurement units.

“The SI redefinition is a landmark moment in scientific progress,” said Martin Milton, Director, International Bureau of Weights and Measures (BIPM).

“Using the fundamental constants we observe in nature as a foundation for important concepts, such as mass and time, means that we have a stable foundation from which to advance our scientific understanding, develop new technologies and address some of society’s greatest challenges,” said Milton.

“Today marks the culmination of decades of work by measurement scientists around the world, the significance of which is immense,” said Barry Inglis, Director of the International Committee for Weights and Measures.

“We will now no longer be bound by the limitations of objects in our measurement of the world, but have universality accessible units that can pave the way to even greater accuracy, and even accelerate scientific advancement,” said Inglis.

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.

Although the size of these units will not change, 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.