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Body Mass Index

What is BMI?

What is it used for?

Body Mass Index (BMI) is a person's weight in kilograms divided by the square of height in meters. A high BMI can be an indicator of high body fatness though it is not diagnostic of body fatness. This is because it does not take into account body composition. Therefore, individuals with high amounts of muscle mass might have a higher BMI since muscle weighs more than fat. However, for the general population, BMI is an inexpensive and easy-to-perform method of screening for weight category such as underweight, normal or healthy weight, overweight, and obesity.

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How is BMI interpreted for adults?

For adults 20 years old and older, BMI is interpreted using standard weight status categories. These categories are the same for men and women of all body types and ages.

The standard weight status categories associated with BMI ranges for adults are shown below:

BMI below 18.5 = Underweight
BMI between 18.5 to 24.9 = Normal or Healthy Weight
BMI between 25 to 29.9 = Overweight
BMI above 30 = Obese


How good is BMI as an indicator of body fat?

The correlation between BMI and body fat is fairly strong, but even if two people have the same BMI, their level of body fat may differ.

  • At the same BMI, women tend to have more body fat than men.
  • At the same BMI, Blacks have less body fat than do Whites, and Asians have more body fat than do Whites.
  • At the same BMI, older people, on average, tend to have more body fat than younger adults.
  • At the same BMI, athletes have less body fat than do non-athletes.

To determine if a high BMI is a health risk, a healthcare provider would need to perform further assessments. These assessments may include skin fold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings.