Well, I used the following metrics: employed professional (50-100)- middle class; upper level professionals, middle managers and lower level executives - (120-250) - upper middle; higher level executives and top professionals, such as top level physicians and lawyers (250+) - upper class, with some correction as to the area (the incomes are area dependent, too). The upper class cannot be too small numerically, that's why I'd think that its lower boundary should be drawn reasonably low. This country has about 7 million millionaires by net worth (not by income), and I would think that 7 million is a good estimate for the size of the upper class.
The lower middle and the middle middle classes have always been the majority.
The upper middle class is neither fish nor fowl nor good red meat...to steal from Shakespeare a bit. They only seem "rich/wealthy" to those below them, but aren't, to the wealthy. And area matters a very great deal! The more expensive an area one lives in, the higher the salary is, for ALL levels. In N.Y.C., for example, a teacher married to a fireman, will have an income of around $100,000; sometimes more. That's hardly well off there.