One way to find out if adults are undernourished is to calculate Body Mass Index (BMI). Take the weight of the person in kg. Then take the height in meters. So, option 3 is correct. Divide the weight by the square of the height. If this figure is less than 18.5 then the person would be considered undernourished. However, if this BMI is more than 25, then a person is overweight. This criterion is not applicable to growing children.