Whether you have high blood pressure, high cholesterol or are worried about carrying excess pounds, you may be interested in quantifying your weight by calculating your Body Mass Index, or BMI. The definition of a normal, or healthy, BMI, depends in part on your height.
Calculating Your BMI
To calculate BMI, divide your weight in kilograms by your height in meters squared. If you prefer not to use the metric system, you can divide your weight in pounds by your height in inches squared, and then multiply the product by 703.
Adult Men and Women
For adult men and women age 20 and older, health professionals apply the BMI to weight status categories of underweight, normal, overweight and obese. A BMI below 18.5 is considered underweight, a BMI of 18.5 to 24.9 is considered normal weight, and a BMI of 25 to 29.9 is considered overweight. BMIs of 30 and above are considered obese.
Children and Teenagers
While BMI calculations for children and teenagers are the same as for adults, BMI is both age- and sex-specific for children and teens. Doctors and pediatricians plot a young patient's BMI on the Centers for Disease Control and Prevention BMI-for-age chart to derive a percentile value. This percentile gives the relative ranking of a child or teen's BMI among young people of the same sex and age. With these percentile rankings, a BMI that falls under the 5th percentile is considered underweight, one that falls in the 5th to 85th percentile is considered a healthy weight, and a BMI falling in the 85th to 95th percentile is considered overweight. A BMI in or above the 95th percentile is considered obese.
Accuracy of BMI
While the CDC maintains that BMI is a reliable measure of body fatness, some researchers have questioned its accuracy. In a study published in the June 2008 issue of the "International Journal of Obesity," authors Abel Romero-Corral et al. concluded that the accuracy of BMI as a tool for diagnosing obesity was limited, especially for people in the intermediate BMI range, men and the elderly. A study by Dale Okorodudu et al. published in the May 2010 issue of the same journal found that BMI was accurate in diagnosing obesity but not in diagnosing excess body fat. The CDC does acknowledge that BMI is not a diagnostic tool for determining health, and that normal BMI-related changes will occur between the sexes and as children and younger people grow.
References
- Centers for Disease Control and Prevention: About BMI for Adults
- Centers for Disease Control and Prevention: About BMI for Children and Teens
- "International Journal of Obesity"; Accuracy of Body Mass Index in Diagnosing Obesity in the Adult General Population; Abel Romero-Corral, et al.; June 2008
- "International Journal of Obesity"; Diagnostic Performance of Body Mass Index to Identify Obesity as Defined by Body Adiposity: A Systematic Review and Meta-Analysis; Dale Okorodudu, et al.; May 2010
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