Well, three to four paragraphs with proper punctuation, capitalization and grammar. It has to be a good size with enough meat to not only tell us about your character but also how they see things around them and the people they interact with. You have to give people something they have flexibility in working with. Like if you look at kingdomkeylight's last post, he is even iffy on it and it a good hearty size. So it's not just size, but what's in it.