Ah, the age old arguments!!
Back in the prehistoric era, when all "lead soldiers" were considered to be toys, the measurments were to the eyes. This was done for the above stated reason that once the figure had head gear, the top of the head was only a theoretical point somwhere in the depths of the figure. So, the eyes had it.
But, when you measure your kid or somebody else, you don't measure them to the eye! That is ridiculous. We measure people to the top of the head because that is how tall they are! Duh.
So, that is the beauty of being a sculptor. I can ignore all of the silly confusion that this simple question can engender and just get down to the business of making models. I started out as a model builder. So, I tend to think in scales and equate them with relative sizes.
As Bob said, 54mm is a size, not a scale. But it is a mean average (to the top of the head, not the eye!) for a guy in 1/32 scale too. Every scale has its mean averages: 1/24 scale - 75mm; 1/18 scale - 100mm; 1/16 scale - 110mm; 1/12 scale - 150mm; 1/9 scale - 200mm; 1/6 scale - 300mm etc.
Some of these "averages are closer to 6 feet tall and some are closer to 5' 10", which is closer to a reasonable average height for a figure. The REALLY important thing is when it comes to scaling weponry and equipment. These things have a very specific size in reality. And that is why it is MORE important to work in a SCALE rather than skewing to some arbitrary size.
But many of the European manufacturers still adhere to the "traditional" standards, which turn out not to be standards at all! This is bogus. It is arbitrary, confusing, unhelpful and results in figures that have no true standard. They come in sizes and scales that are all over the map. Balderdash!
I work to a scale. I rough guesstimate the height of a given figure, sometimes add a few millimeters if I want to "idealize" the proportions and run with that. But all of my rifles and swords and such are made to a specific scale, usually those quoted above. No muss, no fuss.
But don't expect my figures to agree with European "standards" or those of anybody else. That is because those "standards" are a huge steaming pile of B.S. There are no standards. I think that figure producers should think of their figures as scale models and get rid of the arbitrary confusion their "traditional standards" create.
But hey, that's just me......
Bonehead