New SI

"New SI" or "quantum SI" are terms used to refer to a series of proposed changes in the International System of Units (SI), which will lead to the redefinition of the kilogram and up to three other base units in terms of fundamental physical constants. The changes will not take effect until the 24th meeting of the General Conference on Weights and Measures (CGPM) in autumn 2011 at the earliest.

The main object of "new SI" is to find an alternative for the International Prototype Kilogram as a mass standard. The kilogram is the only one of the SI base units still to be defined in terms of a prototype standard, and intercomparison of national prototypes suggests that the stability of these standards is not as great as had previously been assumed. The favoured option is to redefine the kilogram in terms of a defined value of the Planck constant. At the same time, the redefinition of the mole, the ampere and the kelvin (in terms of the Avogadro constant, the elementary charge and the Bolzmann constant respectively) is also under consideration.