Body Mass Index (BMI) is a measure of a person's weight in relation to height, not body composition.
Body Mass Index
Between 20 and 25 is considered ideal
Below 18.5 indicates underweight
Between 25 and 29 indicates overweight which can lead to health problems
30 or higher, experts consider an indicator of obesity which is dangerous to your health
These values do not apply to athletes and body builders, pregnant and nursing woment, the frail or elderly or people under 18.