Body mass index (BMI) is an index of weight-for-height commonly used to classify overweight and obesity. It is defined as a person’s weight in kilograms divided by the square of his/her height in meters (kg/m²). In adults, overweight is defined as a BMI of 25 or more, whereas obesity is a BMI of 30 or more. Among children and adolescents, BMI thresholds for overweight and obesity vary by age. (Source: WHO)