Body mass index

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Body mass index (abbreviated BMI) is a rough measure of proportionality between a person's height and weight, and is used to estimate whether a person is at a healthy weight for their height. BMI is calculated as weight in kilograms divided by height in meters squared. For english units, a conversion factor is applied.

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Healthy BMI is between 18.5 and 24.9. Less than 18.5 is considered underweight; between 25 and 29.9 is considered overweight, over 30 is considered obese, and over 45 is considered morbidly obese.

A BMI over 25 or less than 22.5 is associated with increased mortality.[1]

BMI chart for adults

PD U.S. Department of Health and Human Services. http://www.health.gov/dietaryguidelines/dga2005/healthieryou/html/chapter4.html
Find your BMI.

Limitations and alternatives

The BMI may overestimate percentage of body fat in athletes and others who have a muscular build, and may underestimate percentage of body fat in older persons and others who have lost muscle mass.[2]

Another limitation is in the choice of exponent. If humans scaled proportionally in all three dimensions as they become taller, the appropriate exponent would be 3, instead of the 2 used for BMI calculation. However, 2 is too low. Data from the United States indicates that an exponent of 2.6 is most appropriate.[3] Relatedly, the government of Singapore has set different cutoff levels of BMI, based on the shorter average stature and somewhat different body shape of Southeast Asians as compared to Europeans.[4]

An alternative anthropometric measure is the waist-to-hip ratio.

Notes