I use the official levels of the Cadre Européen Commun de Référence pour les Langues, the Common European Framework of Reference for Languages. The levels: A1 (beginner) A2 (pre-intermediate) B1, B2 (intermediate) C1, C2 (advanced). I added one, that I named R for "Racines", which means "Roots". It corresponds to complete beginner in French, and aims at providing a solid foundation on which to build.
How do I know my level?
If you are currently attending a French language programme, or studying at a University, you probably know your level. For all the other free learners, just pick what you think might be your level and experiment. You can self-assess your level by selecting a type of exercise entitled "Test", which mixes various grammar, vocabulary, cultural points.
If you find the "test" you are taking too challenging, move to the previous level, if you find it easy, just go up to the next level. (I'm working on putting up a bunch of tests, so if you visit regularly you should find a test for you).