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How do you calculate body mass index (BMI)?

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Quick Answer

Body mass index, or BMI, can be calculated using the following equation: weight / {(height)^2 x 703}, according to the Centers for Disease Control. In this equation, weight is measured in pounds and height is measured in inches.

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Full Answer

A person's body mass index, or BMI, is a number that is calculated directly from a person's height and weight, according to the Centers for Disease Control. The calculation can determine how much body fat a person has, even though it is not calculated from a direct measurement of a person's body fat. Even so, BMI calculations are considered to be accurate representations of a person's body fat and are easy screenings for patients to determine if they are overweight, average or underweight.

In medical settings, BMI calculations are used as screening tools to identify weight issues in adults, according to the Centers for Disease Control. BMI ranges can also be determined to allow patients to see what weight ranges they should stay within to be considered in a healthy weight range. According to generic BMI readings, any person with a BMI over 25 is considered to be overweight, while anyone who has a BMI over 30 is considered to be obese.

Although BMI is widely used as a health metric, it is not always accurate, reports Keith Devlin of NPR. The formula used to calculate BMI does not take a person's waist size into account even though waist size directly correlates to how overweight or obese someone is. The formula also fails to account for how much bone and muscle are in the body. Because bone weighs more than fat and muscle, muscular people with strong bones have high BMI values even if they have very little fat on their bodies.

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