Body Mass Index (BMI) is one useful tool in assessing your body's overall health.  It provides a reliable
indicator of body fatness for most people and is used to screen for weight categories that may lead to
health problems.  BMI can be considered an alternative for direct measures of body fat.  The number
calculated from a person's weight and height.

 BMI = (kg) / (m²)

Calculating BMI is one of the best methods for population assessment of overweight and obesity. Because calculation requires only height and weight, it is inexpensive and easy to use for clinicians and for the general public. The use of BMI allows people to compare their own weight status to that of the general population.


Interpretation of BMI for adults

For adults 20 years old and older, BMI is interpreted using standard weight status categories; men should be between 20-25 and women should be between 18-22. 

The standard weight status categories associated with BMI ranges for adults are shown in the following table.

The correlation between the BMI number and body fatness is fairly strong; however the correlation varies by sex, race, and age. At the same BMI, women tend to have more body fat than men.  And older people, on average, tend to have more body fat than younger adults.


It is also important to remember that BMI is one factor related to risk for disease. For assessing someone's likelihood of developing overweight- or obesity-related diseases,for example, high blood pressure, physical inactivity, Coronary heart disease, diabetes and stroke.

 
Reference from Centers for Disease Control and Prevention / healthweight