Even the Washington Post admits there sort of is no such thing, because standards vary across the world. But broadly speaking, you have enough for the essentials and then a little extra to spend discretionarily. The concept really allows us to instead benchmark global progress in development. Regardless, yesterday the Post published a calculator that allows you to compare household income across the world to that global middle class.
The catch, however, is that income is priced in US dollars, which is the currency of very few countries. But thankfully, the Post gives the methodology behind the calculator at the end of the piece so you can understand that and the other little quirks, like rural vs. urban China.
From a design standpoint, there is not much to quibble with. I probably would not have opted for red vs. green to showcase global middle and global lower-than-middle class. But the concept certainly works.
Credit for the piece goes to Leslie Shapiro and Heather Long.