The Body Mass Index is used as one of the measurements to assess appropriate body weight. It has become a common term used in medical literature and in patient education, but many are still confused as to what the BMI is and how it is calculated.
History of the BMI
Originally called the Quetelet index after its founder, the BMI is a measurement that estimates healthy body weight based on a person's height. It is currently used in health care as a screening tool for assessing levels of obesity.
Calculation
The formula for metric numbers is weight in kilograms divided by height in meters squared. Using non-metric measurements, the calculation is pounds of body weight x 703 divided by height in inches squared. The same formula is used regardless of gender or age, but children are graphed on a different chart than adults, and BMI is referenced as a percentile rather than a whole number.
BMI Interpretation
Normal BMI is considered to be 18.5 to 24.9, with lower numbers indicating an underweight status. A BMI of 25 or over indicates an excess of total body fat, and an individual with a BMI over 30 is considered obese.
BMI Tables
BMI tables are available as a visual representation of BMI status.
BMI Limitations
The formula may overestimate body fat in those with a muscular build. The formula may also misdiagnose body fat in the elderly and those who have lost muscle mass due to illness.
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