This cartoon from The Seattle Times illustrates how America's economic pizza is actually sliced per capita, highlighting the massive disparity between the Top 1%, the merely wealthy, the upper middle class, and the lower 50%.
The top x% owning y% of combined wealth is a standard measure of wealth inequality. This is literally what the Lorenz curve describes and the basis for the well-known Gini coefficient.
That being said, the proportions in the comic aren't really in line with the figures I know. Wealth inequality is increasing in the US, but the wealth share of the top 1% currently is more like 33% (still bad but far away from the pizza example).