What Is Body Mass Index?...Your Body Mass Index, also known as your BMI, is really just a height to weight ratio. It is a formula used to calculate how your weight compares to what is expected for your height. It is a very flawed estimation in that it does not take into account if you are more fat or muscle. So a man who is 200 pounds and 6 feet tall has a BMI of 27, regardless of whether he is solid muscle or as flabby as a jello mold. Ranges that are generally accepted for normal or ideal weight are 19 to 25, with 25 to 30 considered overweight, 30 to 40 classified as obese, and above 40 as morbidly obese. Expected or ideal weights for women are generally 100 pounds for the first 5 feet and adding 5 pounds for every inch over that, and adding 7 pounds for every inch over for men. So a woman who is 5'5" would have an ideal weight of 125 pounds and a man who is 5'5" would have an ideal weight of 135 pounds. Those values are also quite flawed though, and don't correlate well with many people's actual weights.