Your doctor figures your body mass index, or BMI, using your weight and height. The measure provides a general estimation of your body fat. If you have a high BMI, you may be at a heightened risk of chronic disease because of your weight. You won't find separate BMI formulas for men and women; a healthy level for an adult man or woman is between 18.5 and 24.9. If your BMI is in an unhealthy range, your doctor will likely perform additional screening tests -- such as skinfold caliper measurements, blood tests and waist circumference measurements -- to further assess your health.
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Body Mass Index Equation
A man's body mass index is figured by taking his weight in kilograms and dividing it by his height in meters squared. The formula reads: weight in kilograms / [height in meters x height in meters] = BMI.
To use the American measurements of pounds and inches, you must apply a conversion factor to the equation. Use your weight in pounds, divided by your height in inches squared, and multiply the total by 703 to get your BMI. The formula reads: weight in pounds / (height in inches x height in inches) x 703 = BMI.
Many health and government sites have online BMI calculators in which you can simply plug in your height and weight. These are a simple, fuss-free way to figure BMI.
Consider your BMI results as a screening tool. If your BMI comes up below 18.5, you're considered underweight. If it's 25 to 29.9, you fall into the category of overweight. If your BMI is above 30, it's an indication that you may be obese and at extreme risk of health complications. BMI isn't infallible, however, and may overestimate or underestimate fatness in some men.
Trends for BMI in Men
Certain height and weight ranges generally qualify a man as having a healthy BMI of 18.5 to 24.9. For example, a man who stands 5 feet, 8 inches tall and weighs between 125 and 163 pounds has a healthy BMI. So does a man who is 6 feet tall and weighs 140 to 183 pounds, or is 6 feet, 4 inches and weighs 156 to 204 pounds.
Although BMI isn't calculated or ranked differently for each gender, a man who has the same BMI as a woman will likely have less body fat. Men usually carry more muscle mass naturally. To support pregnancy and breastfeeding, women carry more fat.
Body Mass Index Drawbacks
The BMI calculation is easy to figure, inexpensive and noninvasive, and it's also relatively reliable for much of the population. But the BMI equation can misrepresent some perfectly healthy and fit men as being overfat. If a man has a muscular, stocky build or is an athlete, an abundance of muscle mass can make him weigh more than average. Muscle is a much healthier tissue that doesn't pose the same health risks as excessive fat. Your doctor should be able to look at you and see that your high level of muscle mass is skewing your BMI reading, but he may run additional screening tests to ensure you're in optimal health.
Sedentary or older men may have a gross weight that, when plugged into the BMI formula, shows them as normal, or healthy. However, BMI doesn't directly measure your ratio of fat to lean mass. A "normal" reading for these men may be misleading if they carry more than 20 percent of their weight as fat. Even if your weight is in the healthy range, having too much body fat makes you susceptible to the diseases and complications that affect men who are overweight. For example, you may be at risk for hypertension and metabolic disturbances like type 2 diabetes.
Other Assessments of a Healthy Weight
Other weight screenings can help you determine if you carry a healthy amount of fat. A simple measure of your waist circumference tells you if you have too much visceral, or belly, fat. This fat collects around your middle and acts like another endocrine organ, secreting compounds that raise your risk of disease. A man with a waist circumference of 40 inches or more is carrying too much visceral fat.
More reliable ways to measure the amount of fat on your body include bioelectrical impedance or body fat scales, skinfold thickness measurements, hydrostatic or underwater weighing and DEXA X-ray scans. Not all of these methods are available or convenient, but you may want to seek them out if you desire a more detailed understanding of your body composition. Some fitness centers, hospitals and personal training centers offer equipment and professionally trained staff to conduct these measurements.