BMI (Body Mass Index)

Body mass index (BMI) is a measure of body fat based on your weight in relation to your height, and applies to most adult men and women aged 20 and over. For children aged 2 and over, BMI percentile is the best assessment of body fat.

BMI does not measure body fat directly. However, research indicates that BMI correlates to direct measures of body fat such as underwater weighing and dual-energy X-ray absorptiometry (DXA), and is considered an inexpensive and easy-to-perform alternative for these.1,2,4

Contents of this article:

What is BMI?

How to calculate BMI for adults

BMI calculators and charts

How is BMI used with children and teens?

Health consequences of overweight and obese adults

BMI limitations

You will also see introductions at the end of some sections to any recent developments that have been covered by Medical News Today’s news stories. Also, look out for links to information about related conditions.

Fast facts on BMI

Here are some key points about BMI. More detail and supporting information is in the main article.

Body mass index (BMI) is a measure of relative size based on the mass and height of an individual.

The Quetelet Index was devised by Adolphe Quetelet, a Belgian mathematician, astronomer and statistician, in 1832. It was later termed “body mass index” in 1972 by Ancel Keys.

BMI is a simple, inexpensive and noninvasive surrogate measure of body fat.

Factors such as age, sex, ethnicity and muscle mass are not accounted for in BMI.

For adults 20 years and older, BMI is interpreted by using standard weight status categories that are the same for all ages, and for both men and women.

For children and adolescents between 2-20 years old, BMI is interpreted relative to a child’s age and sex.

BMI is a reasonable indicator of body fat for both adults and children.

Because BMI does not measure body fat directly, it should not be used as a diagnostic tool.

BMI should be used as a measure to track weight status in populations and as a screening tool to identify potential weight problems in individuals.

Other measures of body fat, such as skinfold thicknesses, bioelectrical impedance, underwater weighing and dual energy X-ray absorption, maybe more accurate than BMI.

What is BMI?

BMI is used as a screening tool to indicate whether a person is underweight, overweight, obese or a healthy weight for their height.

If a person’s BMI is out of the healthy BMI range, their health risks may increase significantly.3

BMI values are age-independent and the same for both sexes. However, BMI may not correspond to the same degree of fatness in different populations due to different body proportions.

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