Calculating BMI The body mass index revolves around weight and height. To calculate BMI, divide your weight in pounds by your height in inches squared, then multiply the result by 703. For example, if you weigh 160 pounds and are 68 inches tall, divide 160 by 4,624 which is 68 squared. Multiply the answer, 0.034 by 703 for a BMI of 24.3. What the Results Mean Generally, if you’re at a healthy weight, your body mass index should fall between 18.5 and 24.9 notes the National Heart, Lund and Blood Institute. If your BMI is below 18.5, you could be underweight. On the other hand, a BMI greater than 25.0 is categorized as overweight, while a score above 30 is considered obese. Why The Number Is Important A body mass index in the low range signals that you could be malnourished. Maybe your body isn’t properly absorbing nutrients or maybe you’re just not getting enough calories to support your activity level. Conversely, having a BMI on the higher end alerts your physician that your risks of heart disease, diabetes and certain cancers are higher than someone with a normal BMI. Problems While BMI is a starting point to evaluate your health, it isn’t flawless. For example, it doesn’t account for gender, and women tend to have more body fat than men. So as a woman, even if your body mass index is in the normal range, you could still have a high percentage of body fat. The calculation also doesn’t account for muscle mass. Muscle weighs more than fat, so if you lift weights and have toned muscles, your BMI could be high even if you’re not overweight. Because of these flaws, your doctor also might run lab tests to evaluate your blood cholesterol levels. In addition, he might measure your waist. A wider than average waist is another indicator for obesity and the risk of related diseases.