1. Definition: Body Mass Index (BMI) is one of the ways used by scientists to find out whether adults are undernourished or over-nourished; it relates a person's weight to his or her height. 2. Method of calculation - Step 1: Take the weight of the person in kilograms. Step 2: Take the height of the person in metres. Step 3: Divide the weight by the square of the height. In formula form: $$BMI = \frac{\text{Weight in kg}}{(\text{Height in metres})^{2}}$$ 3. Interpretation: If this figure is less than 18.5, the person is undernourished; if it is more than 25, the person is overweight. (For children a different criterion is used.) 4. Example: If a person weighs 60 kg and her height is 1.5 m, then $$BMI = \frac{60}{(1.5)^{2}} = \frac{60}{2.25} = 26.7$$ Since 26.7 is more than 25, the person is overweight. 5. Use: BMI is thus a simple indicator of the nutritional status and health of the people, and health is an important aspect of development.