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Obesity is an abnormally high proportion of body fat. The doctor can often determine if you are obese by looking at your body and assessing the percentage of body fat. Methods of assessing body fat are discussed below.

Measuring your weight in relation to your height is the traditional way of determining whether you are overweight, obese, or at an appropriate weight. Your doctor can often determine if you are overweight or obese by calculating your body mass index (BMI). This can be done by dividing your weight in kilograms by your height in meters squared. Your BMI can easily be calculated using a height and weight table. The BMI calculation does not take into account whether your weight is composed mostly of fat or muscle. Some muscular people may have a high BMI without being overweight or obese.

In addition, there is risk associated with abdominal fat build up, even if your total weight is not high. So measuring the circumference of your waist is also an important measure of whether you need to lose weight.

There are other tests that can estimate your percentage of body fat. The accuracy of these tests varies and some are so expensive that you are not likely to have them at the doctor’s office. When combined with your visual appearance and waist circumference, your BMI can usually provide a valid estimate of whether you are overweight or obese.

Tests to diagnose obesity include:

  • Body Mass Index (BMI)—A BMI of 25 to 29.9 is considered overweight and 30 or higher is considered obese for adults.
  • Waist circumference, sagittal diameter, and waist-to-hip ratio—Simple measurements that estimate the amount of fat deposited in the skin and inside the abdominal cavity. Waist-to-hip ratio greater than 1 in men or greater than 0.8 in women is considered obese. Waist circumferences that exceed 102 centimeters (40 inches) men or exceed 88 centimeters (35 inches) in women are associated with an increased risk of heart disease.
  • Skinfold caliper—Most fat is deposited beneath the skin. This test measures fat just beneath the skin, but cannot measure fat inside the abdomen.
  • Water displacement tests—Fat floats; the rest of your body tissues sink. Determining how well you float provides an estimated ratio of fat to body mass.
  • Electrical measurements—A couple of tests calculate your percentage of body fat by measuring the difference between the electrical characteristics of fat and other tissues in your body.
  • Blood tests—To rule out other medical conditions that may cause excess body weight, such as thyroid or adrenal disorders


Aim for healthy weight. National Heart, Lung, and Blood Institute website. Available at: Accessed February 27, 2014.

Barlow SE, and Expert Committee: Expert Committee Recommendations Regarding the Prevention, Assessment, and Treatment of Child and Adolescent Overweight and Obesity: Summary Report. Pediatrics. 2007;120(Suppl)S164-S192).

Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. National Heart, Lung, and Blood Institute and The National Institute of Diabetes and Digestive and Kidney Diseases. Available at: Published September 1998. Accessed February 27, 2014.

Deurenberg P, Deurenberg-Yap, Guricci S: Asians are different from Caucasians and from each other in their body mass index/body fat percent relationship. Obesity Rev. 2002;3:141-146.

Deurenberg-Yap M, Schmidt G, van Staveren WA, Deurenberg, P: The paradox of low body mass index and high body fat percentage among Chinese, Malays and Indians in Singapore. Int J Obes Relat Metab Disord. 2000;24:1011-7.

Heart-Health Risk Assessment. American Heart Association website. Available at: Updated November 13, 2013. Accessed February 27, 2014.

How Are Overweight and Obesity Diagnosed? National Heart, Lung, and Blood Institute website. Available at: Accessed February 27, 2014.

Obesity in adults. EBSCO DynaMed website. Available at: Updated February 19, 2014. Accessed February 27, 2014.

Obesity in children and adolescents. EBSCO DynaMed website. Available at: Updated November 8, 2013. Accessed February 27, 2014.

Last reviewed March 2015 by Kim A. Carmichael, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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