Yes, measuring height using the metric system is pretty difficult, same for shoe size. Europeans seem to love doing it, but it's really the only time I don't use the metric system.
While a hypothetical size 0 (European scale) shoe would actually have a length of 0 millimeters, the system is not metric.
The base mass unit was always intended to be the kilogram, so you might wonder why they didn't give it a name of its own. They did, the grave, named after gravité, but the name was judged too similar to a title of nobility, so they axed the name, but kept the gram which had originated as a alternate name for the milligrave to be used with small quantities. (Volume also had two base units, the litre and the stere which was equal to a kilolitre and expected to be used for such things as firewood, ore, or timber.)
Of course, neither problem exists in spoken language as noone calls kilograms anything but "Kilos". And people who deal with large quantities regularly measure them in "Kubik" (short for cubic metre, which is of course the same as a kilolitre. A litre being, technically, a cubic decimetre.)
