Body Calculator - BMI (Body Mass Index) - Body Mass Index (BMI) I a measure of body fat based on height and weight that applies to adult men and women. BMI can be used to indicate if you are overweight, obese, underweight or normal. A score below 20 indicates that you are underweight; while a score above 25 means you may be overweight. Values are shown here fall into following categories: - Underweight - Normal Weight - Overweight - Obese (Class 1) - Moderately obese - Obese