I think it depends on the school. They don't say how many characters are allowed until you go over the limit I think. That's what happened to me at least with Emory's supplemental. one of them was 1200 characters, and it showed up after I put in my response and was over the limit. So I think unless it tells you at some point, I would say there is no particular limit. Although some of the questions do require you to take some time and formulate a well thought out answer that ends up being around 4500 characters (i.e. the autobiography that some schools require). Hope that helps