The international measurement community, through the International Committee on Weights and Measures, is considering updating parts of the SI.

The proposed change, which will probably occur in 2011, will redefine the kilogram, the ampere, the kelvin and the mole in terms of fundamental physical constants. The kelvin, instead of being based on the triple point of water as it is now, will be defined by assigning an exact numerical value to Boltzmann's constant, k (= 1.3806xx 10^-23 J K^-1). The effect will be to define temperature through thermal energy kT, and so link it with the rest of the SI. The definition will be generalised, making it independent of any material substance, technique of realization, and temperature or temperature range, to ensure the long-term stability of the unit.

For almost all users, the redefinition will pass unnoticed; water will still freeze at 0 °C, and thermometers calibrated before the change will continue to indicate the correct temperature.

For further information, see BIPM website and Pathfinder Programme.