Your body mass index, or BMI, is a body fat measurement derived from your height and weight. Although BMI can yield misleading results for some individuals--such as athletes and the elderly--it's a reliable tool for the general population, according to the Centers for Disease Control and Prevention. BMI is also more convenient and accessible than other body fat tests, many of which require expensive equipment and trained personnel to perform. Calculating your BMI can help you determine whether you're underweight, at a healthy weight, overweight or obese.
Step 1
Weigh yourself without shoes, bulky clothing or heavy accessories in order to determine your current weight. A difference of even a few pounds can alter the results of your BMI calculation, so obtaining a precise measurement is important.
Step 2
Measure your height by standing against a wall on a non-carpeted surface--again without shoes--and unrolling a tape measure spanning the length of the floor to slightly above your head. If someone nearby is available to help you, ask him to read the measurement for your height; it may help to slide a book or flat piece of cardboard over the top of your head towards the tape measure to determine the correct number. If you're alone, hold a pencil horizontally against the top of your head and make a light mark on the wall behind you, then measure the distance between the floor and the pencil mark.
Step 3
Divide your weight in pounds by the value for your height in inches squared, then multiply this number by 703. Alternatively, if you used metric measurements for your weight and height, divide your weight in kilograms by the value for your height in meters squared. The final number for either of these formulas is your BMI.
As an example, an individual weighing 140 lbs. at 65 inches tall would calculate her BMI as follows: 140 / (65 x 65) x 703 = 23.3.
Step 4
Determine whether your BMI falls within a healthy range. As the Mayo Clinic states, an adult BMI below 18.5 is considered underweight, a BMI between 18.5 and 24.9 is considered normal, a BMI between 25 and 29.9 is overweight and a BMI of 30 or higher indicates obesity.
Tips and Warnings
- Adult BMI ranges are not accurate for children and teens, whose ideal BMI depends on gender and age. Determining a healthy weight for children requires viewing height and weight tables, such as the CDC's clinical growth charts. Consult a physician if your BMI falls outside the normal range. When obtaining a weight measurement, digital scales are more reliable than spring-loaded models.
- Your BMI is not the only indicator of your risk for developing diseases. Even a normal BMI does not guarantee health if you live a sedentary lifestyle, have high blood pressure or make poor dietary choices. If you're an athlete or have a high degree of muscle mass, your BMI measurement may overestimate your body fat level. Clinical body fat tests, such as skin-fold measurements and bioelectrical impedance, may yield more accurate results. BMI measurements tend to misrepresent the level of body fat in the elderly, who carry a larger proportion of fat than younger individuals.
Things You'll Need
- Scale
- Measuring tape
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