# SI redefinition of the kilogram - what is one measuring? [duplicate]

I have been reading about the new SI units and specifically, want to get a better understanding of the definition of a kilogram. It was written that the kilogram will be defined in terms of Planck's constant $$\mathrm{h}$$, which has a newly accepted value of $$6.626070150 × 10^{-34} \mathrm{kg⋅m^2s^{-1}}$$. Now, I am also aware that Planck's constant relates the energy of a photon to its frequency.

But what does defining the kilogram in terms of Planck's constant mean, exactly? That is, when I measure $$1\mathrm{kg}$$ of a substance, what am I really measuring?

As an example, I read that whenever I measure the length of an object, I am really measuring the time it takes for light to travel between the two points of measurement.