No, I said "top 20% of
income", not "top 20% of income
s". Possibly I should have said "the part of the population that controls the top 20% of income, ordered by the amount each household earns", or words to that effect? It is tricky to word right.
If you swing over to the XKCD
money chart, Randall already did the work.
On the Trillion chart, the US household income section.
The cut off for the "top 20% of income" is a household earning ~400,000$+/year, consisting of ~1.3% of households. So 400k+ is "upper class".
The cut off for the next 20% of income is a household earning ~150,000$+/year, consisting of ~8% of households. So 150k-400k is "upper middle class".
The cut off for the next 20% of income is a household earning ~90,000$+/year, consisting of ~16% of households. So 90k-150k is "middle middle class".
The cut off for the next 20% of income is a household earning ~55,000$+/year, consisting of ~23% of households. So 55k-90k is "lower middle class".
The cut off for the bottom 20% of income is a household earning less than ~55,000$/year, consisting of ~52% of households. So a household income of 55k and below is "lower class".
These are divided into quintiles of "economic strength". Economically, the upper class, the upper middle, the middle middle, the lower middle and the lower class each have about as much "voting power" economically.
We could instead split things into thirds -- upper, middle and lower classes, then talk about 1/3 of each third as upper upper, middle upper and lower upper (etc). Each class (upper, middle and lower) would have about the same total economic power (realized or not) under such a scheme.
Note that under perfect income equality, we'd have 20% of the population in each bucket. Under a (true) absolute economic despotism, we'd have one person in every category, and the rest of the population in the lower classes. (Amusingly, the true economic despot would be the entire upper, upper middle, middle middle, lower middle, and also in the lower class -- but that is sort of a corner case!)