Your BMI, or body mass index, is an indicator of how much body fat you have. Medical researchers use your BMI to determine if you fall within a recommended fitness range. BMI measurements are useful as a guide, but only a medical expert can determine your actual level of fitness. To find your BMI, divide your weight in pounds by the square of your height in inches. Multiply that number by 703. The result is your BMI.
Function
Your weight alone doesn't indicate your fitness level as it pertains to body fat. A BMI also factors in your height, leading to a more precise measurement that allows you to compare yourself to recommended benchmarks. Doctors also have more exacting methods for determining your body fat level, such as using calipers to measure skin thickness, underwater weighing, or performing medical procedures such as dual-energy X-ray absorptiometry or isotope dilution. Because these procedures are often cost-prohibitive and difficult to standardize, a BMI measurement is typically sufficient for general recommendations regarding body fat.
Expert Insight
An online calculator can determine your BMI, plus factor in other data to help you determine your daily energy needs. For example, Baylor College of Medicine provides a calculator that reports both your BMI and an energy-needs estimate that factors in your gender, age, height and activity level. For children and teens, the Centers for Disease Control and Prevention provide an alternate calculator suited to a child's developing physiology. Note that the numbers provided are only rough estimates. Consult a doctor or fitness expert for a more precise measurement and specific health recommendations.
Types
Once you have your BMI, determine which body fat range you fall into. The University of Kentucky provides the following ranges: A BMI below 18.5 is considered underweight. A BMI between 18.5 and 24.9 is normal -- this is the recommended range for most people. A BMI between 25 and 29.9 is considered overweight. A BMI of 30 to 39.9 indicates obesity. A BMI of 40 or above indicates morbid obesity.
Considerations
Your BMI does not measure how much actual fat you have, as the formula is based on your weight, which includes both muscle and fat. Muscle weighs more than fat, so it is possible to be muscular, in good health and have an above average BMI. To determine whether you have too much body fat, visit a doctor or a fitness expert, who will use a variety of measures to determine your current fitness level.
Warning
A high BMI increases your risk of developing hazardous health conditions. Those who are in the overweight, obese or morbidly obese categories have a higher risk of heart disease, diabetes, high blood pressure and several cancers, according to the University of Kentucky.
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