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Defining overweight and obesity


Obesity means having too much body fat. It is not the same as overweight, which means weighing too much. A person may be overweight from extra muscle, bone, or water, as well as too much fat. But both terms mean someone's weight is higher than what is thought to be healthy for their height.

Body mass index

Your body mass index (BMI) and waist circumference (your waist measurement in inches) are the 2 most common ways to measure health risks related to your weight.

BMI is calculated using height and weight. You and your health care provider can use your BMI to estimate how much body fat you have.

Calculate your BMI

To understand how your BMI relates to your weight, use these ranges (people 20 years and older only):


Weight Status

Below 18.5 kg/m²


18.5 - 24.9 kg/m²


25.0 - 29.9 kg/m²


30.0 kg/m² and above


The medical field divides obesity into 3 groups, or classes. Depending on your BMI, you may have:

  • Class 1 (low-risk) obesity, if your BMI is 30 to 34.9
  • Class 2 (moderate-risk) obesity, if your BMI is 35 to 39.9
  • Class 3 (high-risk) obesity, if your BMI is equal to or greater than 40

A BMI of 40 or more usually means men are at least 100 pounds over their ideal weight and women are at least 80 pounds over their ideal weight.

The higher your BMI, the higher your risk for certain diseases such as heart disease, stroke, high blood pressure, type 2 diabetes, sleep apnea (stopping breathing while you are asleep), and arthritis.

See also: Health risks of obesity

If you have more or less muscle than is normal, your BMI may not be a perfect measure of how much body fat you have and therefore not as accurate in judging your risk of obesity-related disease:

  • If you are muscular, you probably have less body fat than your BMI is telling you. In other words, it will overestimate how much body fat you have and be a higher number.
  • If you have less than a normal amount of muscle, your amount of body fat may be higher than your BMI is telling you. In other words, it will underestimate how much body fat you have and be a lower number.
  • Many experts use values of 23.0 - 24.9 and 25.0 and above to define overweight and obesity in Asians.

Waist circumference measurement

Your waist measurement is another way to estimate how much body fat you have. Extra weight around your mid-section or stomach area increases your risk for type 2 diabetes, heart disease, and stroke.

People with "apple-shaped" bodies (meaning their waist is bigger than their hips) also have an increased risk for these conditions.

To measure your waist circumference:

  1. Take off clothing from your waist area.
  2. Stand up straight and wrap a measuring tape around your trunk, just above your hipbones.
  3. Take the measurement with your stomach relaxed as you breathe out.

The risk of obesity-related diseases increases when a man's waist circumference is more than 40 inches and when a woman's waist circumference is more than 35 inches. Men and post-menopausal women are more likely to gain weight in their stomach area.

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Review Date: 7/1/2011

Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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