The standard sizing method I learned, and has served me well was this.
For a beginner your skis should fall between your chin and nose, intermediate should fall between your nose and eyebrows, and expert they should fall between your eyebrows and top of your head, if you like them that long. By the time you are good enough to be considering skis that long, you should have an idea of what you want and the differences each length will make. Keep in mind too if you are riding skis with alot of rocker on the tip and tail, they will handle like much shorter skis.