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What Is Body Mass Index?

what is Body Mass Index

What is Body Mass Index?

BMI is a measure of weight proportionate to height. Generally, BMI is considered an effective way to evaluate whether a person is overweight or obese, though there are exceptions to the rule. Some muscular people may have a BMI that puts them in the overweight range. However, these people are not considered overweight because muscle tissue weighs more than fat tissue.

According to the National Heart, Lung, and Blood Institute (NHLBI), a BMI from 18.5 to 24.9 is considered normal while a BMI of more than 25 is considered overweight. A person is considered obese if the BMI is above 30, and morbidly obese if the BMI is above 40.

BMI Ranges

  • Underweight = 18.5 or less
  • Normal weight = 18.5-24.9
  • Overweight = 25-29.9
  • Obesity = 30 or greater


What is Body Mass Index

About Body Mass Index (BMI)

what is Body Mass Index

What is Body Mass Index?

Body mass index (BMI) is a weight-to-height ratio and is a measure of body fat based on height and weight that applies to adult men and women and is used as an indicator of obesity and underweight.  The Body Mass Index(BMI) formula was developed by Belgium statistician Adolphe Quetelet (1796-1874), and was known as the Quetelet Index. BMI is also referred to as ‘body mass index”.

How Are Body Mass Index Results Interpreted?

For adults 20 years of age and older, a BMI of 18.5 to 24.9 is considered normal, 25 to 29.9 is considered overweight, and a BMI of 30 or higher is considered obese. A person with a BMI under 18.5 is considered underweight; one of the criteria for diagnosing anorexia is a BMI under 17.5.

For children and teens (people under the age of 20), the BMI number is plotted on the BMI-for-age growth charts (for either girls or boys) to obtain a percentile ranking. The percentile indicates the relative position of the child’s BMI result among children of the same sex and age. A healthy weight ranges from the 5th to the 84th percentile.

What Are the Risks Associated With Being Overweight or Obese?

People who are overweight (defined as a BMI between 25.0 and 29.9) or obese (defined as a BMI greater than or equal to 30) are at increased risk for developing a number of medical conditions, including:

  • High blood pressure (hypertension)
  • Heart disease
  • Stroke
  • High cholesterol or other lipid disorders
  • Type 2 diabetes
  • Certain cancers
  • Sleep apnea
  • Osteoarthritis
  • Gallbladder disease
  • Fatty liver disease.


Body Mass Index