- Class 1: BMI of 30 to 34.9
- Class II: BMI 35 to 39.9
- Class III: BMI of 40 and greater
These guidelines are very important for people at risk for diabetes, heart disease, or certain cancers. It is also used to determine treatment approaches such as when surgery may be appropriate. The higher the BMI, the greater the risk for significant health problems.
Calculating Body Mass Index (BMI)One’s body mass index (BMI) is derived by multiplying a person's weight in pounds by 703 and then dividing by the height in inches, then dividing that number by the height in inches. The steps are as follows:
For example, a woman who weighs 150 pounds and is five feet eight inches (or 68 inches) tall has a BMI of 22.8. |
Waist Circumference and Waist-Hip Ratio. The extent of abdominal fat can also be used in assessing risk of disease. Some studies suggest that:
- Women whose waistlines are over 31.5 inches and men whose waists measure over 37 inches should watch their weight.
- A waist size greater than 35 inches in women and 40 inches in men is associated with a higher risk for heart disease, diabetes, and impaired functioning.
Evidence strongly suggests that more body fat around the abdomen and hips (the apple-shape) is a more consistent predictor of heart problems and health risks than BMI.
The distribution of fat can be evaluated by dividing waist size by hip size. For example, a woman with a 30-inch waist and 40-inch hip circumference would have a ratio of 0.75; one with a 41-inch waist and 39-inch hips would have a ratio of 1.05. The lower the ratio the better. The risk of heart disease rises sharply for women with ratios above 0.8 and for men with ratios above 1.0.
 | Click the icon to see a depiction of the waist-to-hip ratio. |
Anthropometry. Anthropometry is the measurement of skin fold thickness in different areas, particularly around the triceps, shoulder blades, and hips. This measurement is useful in determining how much weight is due to muscle or fat.
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