The US's richest 1% own as much as 50% of the country's wealth, the richest 5% own more than 50% of the wealth, the richest 25% own 87% of the wealth, and the poorest 40% own 0.3% of the wealth. The national median net worth is $86,000.
To compare wealth with income, here are income quintiles via Wealth and Poverty: Who's Got How Much?:
in the year 2000:Many people have tried to combine wealth and income to identify the US's class system, and all have acknowledged that any system will have many exceptions. Making that same acknowledgment, I propose this:
20 percent of U.S. households had incomes of $18,000 and under
20 percent had incomes between $18,001 and $33,000
20 percent had incomes between $33,001 and $52,300
20 percent had incomes between $52,301 and $82,000
20 percent had incomes above $82,000
...5 percent of households had incomes of $145,500 and higher. (This 5 percent is also counted in the top 20 percent.)
In the US, the working class is the bottom 50%. Effectively, they own nothing. They fit Marx's definition of the proletariat: they have little or nothing to sell but their labor.
The middle class are the upper 45%. Based on income quintile, call them lower (third quintile), middle (fourth quintile), and upper (fifth quintile) middle class. They make some money from investments.
The top 5% are the upper class, the rich, the bourgeoisie.
And the top 1% are the super-rich, the capitalist class, the people who decide what choices everyone else may have at the polling place and the market place.
Recommended: Why income distribution can't be crowd-sourced. - By Timothy Noah - Slate Magazine
ETA: There are problems with this system. See the discussion at G+. Where do you put sports stars making millions of dollars a year who have to sell their talent? It's why I ultimately like Marx's definitions: Do you own the means of production? If no, you're part of the working class, the proletariat. If yes, you're in the bourgeoisie, the marketers who were the middle class under feudalism who have become the upper class under capitalism. If you're somewhere in between, you're in the petite bourgeoisie, the little imitators of the people who own most of the wealth.