# How To: Figure your body mass index

Less than seven hours’ sleep a night is associated with obesity, according to the journal Sleep. So if you’re interested in losing weight – as well as driving safely, and obeying federal hours rules – park and get some shut-eye.

Your body mass index, or BMI, is a number that assesses your weight relative to your height. It’s widely used as a simple, do-it-yourself indicator of whether adults are obese or, less commonly, underweight. Here’s the formula for calculating BMI:

Weight (pounds) X 703
Height (inches) squared

Online BMI calculators – such as the National Heart Lung and Blood Institute’s at www.nhlbisupport.com/bmi – will do the math for you, once you plug in height and weight.

As a general rule, the higher your BMI, the more likely you are to be obese and the more at risk you are of obesity-related illnesses such as heart disease and diabetes. Here’s how to read the results, according to the National Institutes of Health:

• Less than 18.5: underweight
• 18.5-24.9: normal
• 25-29.9: overweight
• 30 or more: obese

The pulmonary institute’s BMI table shows that a 5-foot adult is normal anywhere from 97 pounds through 123 pounds, while a 6-foot adult is normal anywhere from 140 pounds through 177 pounds.

Because it fails to account for muscle and bone mass, however, BMI is not an infallible body-fat calculation, as any glance at a Major League Baseball roster will demonstrate. Atlanta Braves pitcher Tom Glavine is obese by no one’s standards, even though he’s 6 feet tall and 205 pounds. A short, muscle-bound weightlifter will have a high BMI even if he has very little body fat, as may a very tall person, while an older person’s body fat is likely to be underestimated by a BMI.

Other obesity indicators that must be considered include waist circumference – it should be less than 40 inches for men, less than 35 inches for women – and risk factors such as high blood pressure, smoking and family history.

Like any other medical diagnosis, obesity ultimately is your doctor’s call to make, as are the steps you should take to treat it. But BMI is a simple, free tool for you to monitor the significance of your own weight between doctor’s visits. Remember, even a 10 percent weight loss can reduce your chance of obesity-related illness – and help keep you and your business on the road.

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