It's not a common metric, however, when you free lance right you are often told, "I need a piece about x & y, 500 words long." So based on that 500 words, let's

It's not a common metric, however, when you free lance right you are often told, "I need a piece about x & y, 500 words long." So based on that 500 words, let's say you make $200. So you just made 40 cents a word. But then next article, the editors says "I need a piece about x & y, 800 words" This time you make $400. So instead of trying to explain it like that in these metrics, it makes more sense to just aggregate the numbers together; because the piece lengths vary.