There are degrees to the friend zone:
1 - You are in the friend zone but there is room to get out and get laid casually. She doesn't' talk about other guys in front of you and there is sexual tension at times. Its the only friend zone level to be at because it can actually flip into the awesome friends with benefits zone.
2. Further into the friend zone trap. You probably know a bit of personal information about her. She still doesn't talk about guys in front of you and she has probably thought about making you a long term thing. If she is thinking about you longer term you haven't had sex with her yet.
3. Now we are entering danger territory. There is still an outside chance for sex with the girl. But it is significantly diminished or you have to spend a substantial time apart and then end up together and realize that it needs to happen. You know plenty of information about her and you party together with other friends. She will mention other guys but not in the, oh I want to fuck him kind of way even though that is what she means.
4. 2% chance of sex and you need to both be absolutely hammered and there needs to some other type of tension besides sex. That's the only way its going to work. She thinks of you when there is a crisis and tells all her friends that you are the best but can't manage to help you get laid or into a real relationship. After all, being in the friend zone for the girl has perks, like having Mr. good guy at her beckon whim. You are a proven dependable and understanding person. She talks about guys in front of you and may have recently just ended a longer term relationship which is why she "isn't ready". You know way to much about her and her "isn't ready" really means never.
5. Its over. Pack up your bags and go home. You're never having sex with this girl. She talks about other guys and sex in front of you. You are mr. perfect just not for her and you have talked about this with her before. She explains that she is into dbags who treat her like shit and that's just not who you are. But, hey, you can be her best man.
If I meet one more of her relatives before even getting my wiener touched I'm writing her off as Level 5, The Friend Zone.