Body Mass Index (BMI) is a measurement of a person's weight in relation to his height. It can be used to indicate a person's body fatness and weight status. It is believed that Body Mass Index is a more accurate measurement of a person's body weight status than his actual weight. You can simply input your weight and height information into BMI calculator shown above and click 'Calculate', your Body Mass Index number will be shown on the BMI calculator. You can then compare your BMI number to the Body Mass Index Category table and find out your weight status (underweight, normal or overweight, etc.).