The body mass index (BMI) is a measure of relative size based on the mass and height of an individual. The BMI for a person is defined as their body mass divided by the square of their height—with the value universally being given in units of kg/m2
A frequent use of the BMI is to assess how much an individual’s body weight departs from what is normal or desirable for a person of his or her height. The weight excess or deficiency may, in part, be accounted for by body fat (adipose tissue) although other factors such as muscularity also affect BMI significantly.
| Category | BMI range – kg/m2 | BMI Prime |
|---|---|---|
| Very severely underweight | less than 15 | less than 0.60 |
| Severely underweight | from 15.0 to 16.0 | from 0.60 to 0.64 |
| Underweight | from 16.0 to 18.5 | from 0.64 to 0.74 |
| Normal (healthy weight) | from 18.5 to 25 | from 0.74 to 1.0 |
| Overweight | from 25 to 30 | from 1.0 to 1.2 |
| Obese Class I (Moderately obese) | from 30 to 35 | from 1.2 to 1.4 |
| Obese Class II (Severely obese) | from 35 to 40 | from 1.4 to 1.6 |
| Obese Class III (Very severely obese) | over 40 | over 1.6 |