The simplest way to determine if you're obese is to calculate your body-mass index, or BMI. To check your BMI, you'll need to know your height in inches, and your weight in pounds. Multiply your weight in pounds by seven-hundred and three. Then take your height in inches and square it. Divide the first figure by the second. The resulting number is your BMI. What does that number mean? Usually, the higher your BMI, the higher your percentage of body fat. If your BMI is less than 18.5, you're considered underweight. A BMI between 18.5 and 24.9 is considered normal, while one between 25 and 29.9 equates to being overweight. If you have a BMI of 30 or higher, you're considered to be obese.