Did you try Zipf's law? contents/size/probabliliyt proportional to the reciprocal of rank? It has the unfortunate mathematical property that the sum of 1/n as ngoes to infinity is infinite, but if you cutt off the tail it seems to fit well with experience in a lot of circumstances.

As Lambert Meertens expresesed it, If you classify any kind of thing into categories, and ramk the categories by the number of things in them, it'll turn out to be proportional to 1/n. Not sure if he was stating an empirical law of nature or just telling me what Zopf's law was, though.