Body mass index (BMI) is a measure derived from an individual's height and weight, calculated to provide an estimate of body fat relative to body size. It is calculated by dividing a person's weight in kilograms by the square of their height in meters. The index value is used in health sciences to categorize individuals into weight ranges, such as underweight, normal weight, overweight, or obese. While it provides a standardized ratio for screening purposes, the calculation itself only accounts for overall mass and height and does not provide direct measurements of body composition, such as the percentage of muscle mass or subcutaneous fat. It serves as a widely recognized, non-invasive screening tool within clinical settings.