Body Mass Index (BMI)
Body mass index, or BMI, is an index for relating height to weight. In short, this tool will tell you whether or not you are overweight.
If you are just setting out to lose weight, and are the sort of person who will be discouraged learning that you are overweight or obese, you may want to avoid using this tool at this point. However, if you can allow yourself to be motivated by bad news, this is an important place to start. Personally, I beleive that knowing is better than not knowing.
If you have acheived or are well into to your weight loss goals, you may want to use the BMI tool as a way to get affirmation for all your hard work. If that is the case, good for you. Don't forget to give yourself a pat on the back.