How many polygons in a piece of string? (thanks, Rick).
There is no real answer to this often asked question without you being incredibly specific and at that point you'll have answered the question yourself. (And, really, some quick searching/google would probably have pulled up the tons of threads asking the same question and told you exactly that, you might want to try looking for answers before asking questions in future).
You could always just try simply looking at the models that come with games and the documentation that comes with their editors. Nearly all of the major titles come with editors and SDKs that allow you to open and view all of the existing game content.