Middle Class is determined by a middle ranking income.
When defined by the federal government, that's what is used.
Which is one more reason the federal government is a lousy answer to economic problems. If you think that local cost of living does not factor into the economic status of people, then you are deliberately blinding yourself.
If one lives in a place where a 3 bedroom home costs around $150,000, a loaf of bread is $1.50 a gallon of milk $2.75, and a gallon of gas in $3.89 then an income of $60,000 will allow a rather nice standard of living. But if one lives in an area where a 3 bedroom house runs $500,000, then $60,000 is not going to allow as high a standard of living. If one lives in a place like rural Alaska, where a loaf of bread is $3.00, a gallon of milk $4.25, and a gallon of gas $5.50, then again the standard of living from a $60,000 income will not be as high as where the COL is lower.
Unlike the government, PEOPLE judge "middle class" by their standard of living, not by some narrow definition of income.
And damned few people these days know what the fuck POOR means, either. Too many define "poor" as those who have to buy their TVs from a second hand store. Bullshit. TVs are a luxury. When one can afford luxuries - even second hand luxuries - then they are not nearly as poor as most are willing to define.
Poor is a family of 6 (plus Grandmother) living in a 2 room shack. Poor is when poaching a deer and squatting on a plot of land to grow some vegetables, and sneaking in fields at night to gather the grain the harvester missed are the means used to barely feed the family. Poor is not worrying about whether your TV is second hand or not, because you don't have electricity to run the damn thing.
Poor is NOT because one uses second hand furniture in a 3 bedroom, rent subsidized apartment. Poor is NOT because one has to choose between paying for cable, or buying TV dinners.