What is Body Mass Index and How to Calculate BMI


Get answers to frequently asked questions about Body Mass Index (BMI).

What is BMI?

BMI stands for Body Mass Index, also commonly referred to as Body Mass Indicator. It’s a number that shows body weight adjusted for height. Body Mass Index is used to indicate if you are normal, overweight, obese, or underweight. BMI for adults is not gender specific. See also BMI Graph (Weight to Height Graph).

Please note that BMI does not measure body fat and muscle mass. If you have large muscle mass and low percent of body fat, you may still have the same BMI as a person who has more body fat and less muscle mass.

Note:BMI does not apply to pregnant and nursing women.

What is a healthy BMI?

For adults aged 20 years or older, BMI falls into one of these categories:

  • Underweight (below 18.5)
  • Normal (from 18.5 to 24.9)
  • Overweight (from 25 to 29.9)
  • Obese (over 30)

The Federal Obesity Clinical Guidelines released by the National Heart, Lung, and Blood Institute define overweight as a BMI of 25 to 29.9 and obesity as a BMI of 30 and above. The guidelines’ definition of overweight is based on research which relates body mass index to risk of illness.

If you fall into the BMI range of over 25 and have a waist size of over 40 inches for men and 35 inches for women, you are considered to be at especially high risk for health problems. To be on the safe side, see your doctor for a complete evaluation.

Is BMI interpreted differently for children and teens than adults?

Yes, it is. BMI for children and teens (2 – 20 years) is gender and age specific. BMI for children is plotted on growth charts. To get the charts and learn about their interpretation, visit National Center for Health Statistics.

How to calculate BMI? What is BMI calculation formula?

BMI = 703 x Weight in Pounds / (Height in Inches x Height in Inches)

BMI = Weight in Kilograms / (Height in Meters x Height in Meters)

Where do I get more information on BMI?

Centers for Disease Control and Prevention: What Does BMI Mean?
Explains that BMI is only one piece of a person’s health profile. Talk with your doctor about other measures and risk factors such as waist circumference, smoking, physical activity level, and diet.

Body Mass Index Studies

“Adolescent BMI Trajectory and Risk of Diabetes versus Coronary Disease.” Amir Tirosh, M.D., Ph.D., Iris Shai, R.D., Ph.D., Arnon Afek, M.D., M.H.A., Gal Dubnov-Raz, M.D., Nir Ayalon, M.D., Barak Gordon, M.D., Estela Derazne, M.Sc., Dorit Tzur, M.B.A., Ari Shamis M.D., M.P.A., Shlomo Vinker, M.D., and Assaf Rudich, M.D., Ph.D. N Engl J Med 2011; 364:1315-1325


1 thought on “What is Body Mass Index and How to Calculate BMI”

  • Thank you for stressing out that BMI does not measure body fat and muscle mass. I really thought it does. Glad that I have read your post. Everything was helpful and the links are a plus in providing a more extensive information about the subject.

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