Body Mass Index (BMI) and Waist Circumference

BMI and Waist Circumference Indicators provide a more accurate measure of total body fat and inherent health risks than weight alone. BMI has an advantage over "percent above ideal weight" (based on Metropolitan life Insurance Tables). Ideal body weight tables such as the Metropolitan Life Insurance tables were developed primarily from white, higher socioeconomic status populations and have not been documented to accurately reflect body fat content in the public at large. In addition, separate tables are required for men and women. The weight tables are based on mortality outcomes and do not necessarily predict morbidity.

BMI

BMI is recommended as a practical approach for the clinical setting. BMI provides an acceptable approximation for assessment of total body fat for the majority of patients. And its limitations must be recognized — it overestimates body fat in persons who are very muscular and can underestimate body fat in persons who have lost muscle mass (the elderly). 5 to 10% of people measured by BMI could be mistakenly classified as overweight or obese. And some people with low BMIs, such as the elderly, can have more body fat than they should.

How to Determine Your BMI

Use the formula below, OR try our new Online BMI Calculator.

BMI is calculated as weight divided by height squared, usually in kilograms and meters. To estimate BMI using pounds and inches: measure your height in inches and multiply this number by itself. Weigh yourself (in pounds) and divide by your height squared (which you just calculated). Now multiply the result by 703. Find that number in one of the ranges in the right-most column below. BMI at 40 or over is considered to be morbidly obese.

Obesity Classification	BMI (kg/m2)	Obesity Classification	BMI (kg/m2)
Underweight	<18.5	Obesity I	30-34.9
Normal	18.5-24.9	Obesity II	35.0-39.9
Overweight	25.0-29.9	Extreme Obesity III	>40

Source: Preventing and Managing the Global Epidemic of Obesity. Report of the World Health Organization of Obesity, WHO, Geneva, June, 1997.

Waist Circumference

The presence of excess fat in the abdomen (what some call "bad body fat") out of proportion to total body fat is an independent predictor of risk factors and morbidity. Waist circumference is positively correlated with abdominal fat content. It provides a clinically acceptable measurement for assessing a client's abdominal fat content before and after treatment.

A high waist circumference is associated with an increased risk for type 2 diabetes, hypertension, and coronary vascular disease (CVD) in patients with a BMI in the range between 25 and 34.9 kg/m2. Fat located in the abdominal region is associated with greater health risks than that in peripheral regions. Waist circumference is a better indicator of relative disease risk than BMI. It also assumes a greater value for estimating risk for obesity-related disease at older ages.

Excess weight and obesity in a patient is of medical concern because it increases the risk for several diseases, particularly cardiovascular diseases (CVDs) and diabetes mellitus while increasing total rates of mortality.

Waist circumferences with increased relative risk are defined as follows:

High Risk

Men: >102 cm (>40 in.)

Women: >88 cm (>35 in.)