How Do I Know if I'm Obese?

Definition of Obesity

Woman standing on scale weighing herself
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What is Obesity?

We often hear that rates of obesity are increasing in the United States and other industrialized countries, and how avoiding obesity can help your longevity whether you’re male or female. But how exactly is obesity defined?

According to the U.S. National Institutes of Health, obesity is having too much body fat. The question then is how much is too much body fat, and how do they determine who has too much body fat?

What measurements are used and do they relate to health and longevity or simply to appearance?

Body Mass Index as a Definition of Obesity

The most common way of gauging obesity is through a measure called the Body Mass Index, or BMI, which is a ratio of body weight to height. The formula, described by the U.S. Centers for Disease Control and Prevention (CDC), is:

BMI = weight (kg) / [height (m)]²

  • Calculate your BMI: If you know your height and weight, use this online calculator to find your BMI number. You can use English or metric units - pounds or kilograms, inches or centimeters.
  • See if your BMI is in a healthy range: this chart will show if you are underweight, normal weight, overweight, or in obese classes I, II or III.

A BMI of 30 or higher is considered obese.

While BMI assessment has some shortcomings, like not accurately accounting for body composition in very muscular people, it's an inexpensive and readily-available tool to compare a person’s weight with that of the general population.

Being obese is being above the weight considered healthy for your height, but it is more important that you have a percentage of body fat to lean tissue that is in a healthy range. The BMI only indirectly measures this. However, unless you are objectively muscle-bound, it's likely that if your BMI is high, you have extra fat weight rather than too much muscle for your height.

If you look in the mirror and see big guns and a six pack and you have a high BMI, you're not obese. But if your BMI says you're obese and you have a poochy belly, it's probably telling you the hard truth.

Other Measures of Adult Obesity

Other more complicated measurements, such as skinfold thickness and bioelectrical impedance, require specialized instruments and expertise to perform, and may therefore be less accessible to the public, according to the CDC.

However, many inexpensive body fat scales use bioelectrical impedance and show their users whether they are in the normal, overweight or obese range. Some of them communicate with apps via Bluetooth so users can track their gain or loss of weight, body fat, water, and lean muscle.

Defining Childhood Obesity

Obesity in children and teens is defined as being at the 95th percentile or greater compared to others of their age and sex. Overweight is defined as being between the 85th and 95 percentile. You can find a BMI calculator for children and teens on the CDC website.


About BMI for Adults. US Centers for Disease Control and Prevention. Public Information Sheet.

Obesity. US National Institutes of Health Medline Public Information Sheet.

Obesity, Physical Activity, and Weight-Control Glossary. US National Institutes of Health Weight Control Information Network Public Information Sheet.

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