Known as BMI, the body mass index is a value derived from the mass (weight) and height of an individual, commonly used to quantify a person's amount of tissue mass. A person can be categorized as underweight, normal weight, overweight, or obese based on that value.
less than 18.5: underweight
18.5 - 25: normal weight
25 - 30: overweight
more than 30: obese