The index that is used to compare nutritional level is called Body Mass Index (BMI), and it is derived from the weight (mass) and height of an individual. The BMI is defined as the body mass divided by the square of the body height and is universally expressed in units of kg/m², resulting from the mass in kilograms and height in meters. It categorizes individuals as underweight, normal weight, overweight or obese based on the derived value.