A redefinition of SI base units is scheduled to come into force on 20 May 2019. The kilogram, ampere, kelvin, and mole will then be defined by setting exact numerical values for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively.

SI units redefinition diagram

Read more
Nature 550, 313 (2017)
PhysicsWorld — SI gets a makeover
The Verge — New definition of kilogram