How do you know what the correct height of your bicycle seat is? Listen to your body. Avoid injuries.
Once youâ€™ve used one of these formulas to get your saddle within a safe range, listen to your body to determine if you need to make small adjustments. Conventional wisdom says pain in the front of the knee indicates a saddle thatâ€™s too low, and pain in the back of the knee indicates a saddle thatâ€™s too high. This has been consistent with my experience. Many people may find their saddles were too low prior to using these methods (Rivendellâ€™s Grant Petersen says 80% of the riders they see have their saddles adjusted too low). If youâ€™re one of these people, give yourself time to adjust to the new position; it will feel strange at first, but in the long run youâ€™ll be doing your knees a favor.
from Eco Velo