(Link) I don’t know what kind of organisation the group „citizen’s for tax justice“ are. So I would not rely too much on the information – but in case they are reporting correct figures for the averge US income (and the ranges seem not implausible – note: not GDP/capita but income per working person) on this website that I found today, then it would be even more astonishing that 19% of Americans believe they are in the top 1% income range and another 20% believe they will be there at some point.
According to the figures reported on the page, the average income for the top 1% of tax payers in the USA in 2001 was 1,028,000 USD. Thus given the usual outliers, I think the top 1% will start somewhere between 400,000 and 500,000 USD, as the avergae top 5% income is 204,000 USD. The general average is 56,500 USD – again, according to this source.