Articles - BMI (body mass index)

What does BMI mean?

Body Mass Index is a number which shows body weight adjusted for height.  The normal ranges for adults over 20 years old are:

• < 18.5 — underweight
• 18.5-24.9 — normal
• 25-29.9 — overweight
• > 30 — obese

BMI is one of the best ways to compare an individual’s weight to the general population.

How do you calculate BMI?

There are several methods to measure obesity which are highly accurate i.e. underwater weighing, bioelectrical impedance, or calipers, but they are expensive, not easily available, or need highly trained personnel to perform correctly.

BMI calculation may be done with either metric or English standard measurements.  The equation most often used is:

{Weight (in pounds) x 704} ÷ Height (in inches) x Height (in inches) = BMI

For example, a 6 ft tall man or woman weighing 180 pounds would have a BMI of:

180 x 704 = 126,720, ÷ by 72 = 1760, ÷ by 72 = 24 BMI 

Often athletes may have BMI of less than 25 due to their muscle mass.  Are they “overweight”?  Yes, they are still considered overweight, but this does not necessarily mean they have too much fat.  Most studies look at the relationship between BMI and risk of disease—NOT body fat percentage and risk of disease.  So we don’t know if 2 people with the same BMI and different amounts of body fat have different risks for disease.