Measuring a person’s body fat percentage can be difficult, therefore, other methods are relied on to diagnose obesity. Two widely used methods are weight-for-height tables and body mass index (BMI). While both measurements have their limitations, they are reasonable indicators that someone may have a weight problem. The calculations are easy, and no special equipment is required.
Most people are familiar with weight-for-height tables. Doctors and nurses (and many others) have used these tables for decades to determine if someone is overweight. The tables usually have a range of acceptable weights for a person of a given height.
One small problem with using weight-for-height tables is that doctors disagree over which is the best table to use. Several versions are available. Many have different weight ranges, and some tables account for a person’s frame size, age and sex, while other tables do not.
A grave limitation of all weight-for-height tables is that they do not distinguish between excess fat and muscle. A very muscular person may appear obese, according to the tables, when he or she in fact is not.
What is the body mass index (BMI)?
The body mass index (BMI) is a new term to most people. However, it is now the measurement of choice for many physicians and researchers studying obesity.
The BMI uses a mathematical formula that accounts for both a person’s weight and height. The BMI equals a person’s weight in kilograms divided by height in meters squared (BMI=kg/m2).
The BMI measurement however, poses some of the same problems as the weight-for-height tables. Not everyone agrees on the cutoff points for “healthy” versus “unhealthy” BMI ranges. BMI also does not provide information on a person’s percentage of body fat. However, like the weight-for-height table, BMI is a useful general guideline and is a good estimator of body fat for most adults between the ages of 19 and 70 years of age. However, it may not be an accurate measurement of body fat for body builders, certain athletes, and pregnant women.
It is important to understand what “healthy weight” means. Healthy weight is defined as a body mass index (BMI) equal to or greater than 19 and less than 25 among all people aged 20 or over. Generally, obesity is defined as a body mass index (BMI) equal to or greater than 30, which approximates 30 pounds of excess weight. Excess weight also places people at risk of developing serious health problems.
The table below has already done the math and metric conversions. To use the table, find the appropriate height in the left-hand column. Move across the row to the given weight. The number at the top of the column is the BMI for that height and weight.
Body weight in pounds according to height and body mass index.
Below is a table identifying the risk of associated disease according to BMI and waist size.
|BMI||Category||Waist less than or equal to 40 in. (men) or 35 in. (women)||Waist greater than 40 in. (men) or 35 in. (women)|
|18.5 or less||Underweight||N/A||N/A|
|18.5 - 24.9||Normal||N/A||N/A|
|25.0 - 29.9||Overweight||Increased Risk||High Risk|
|30.0 - 34.9||Obese||High Risk||Very High Risk|
|35.0 - 39.9||Obese||Very High Risk||Very High Risk|
|40 or greater||Extremely Obese||Extremely High Risk||Extremely High Risk|
Revision date: June 11, 2011
Last revised: by Jorge P. Ribeiro, MD