From the link, the problem:
Now physicists want to do the same for the kilogram, which is currently defined as the mass of a cylinder of platinum and iridium called the International Prototype Kilogram.
That’s a problem because each time it is picked up, a few atoms rub off the cylinder making it imperceptibly lighter. For this reason almost nobody is allowed to measure the mass of the International Prototype Kilogram, which is stored in a vault in Sevres in France. So nobody really knows how much mass the kilogram is losing or indeed, whether it is gaining the weight of a thin layer of dust and impurities which must surely be gathering on its hundred year-old surfaces.
And one proposed solution:
So Fox and co have another suggestion. Why not make the kilogram equal to the mass of a certain number of carbon-12 atoms, specifically 2250× 28148963^3 of them?
Then a kilogram would be a cube of carbon 8.11cm on each side (8.11cm is roughly the length of 368,855,762 carbon atoms laid side by side).
With that definition, almost anybody could make a kilogram in their own kitchen given some carbon and a knife.
“The day we made a kilogram” might even be the kind of fun that could engage and inspire a new generation of scientists, which ought to be a good enough reason on its own on which to decide.
Note: it’s totally worth hitting the link just to read the comments.