Although a variety of measurements are available to assess how healthy your weight is, your body mass index -- also known as your BMI -- is one of the most common. Calculated from your weight relative to your height, the BMI scale can help estimate your level of body fat, as well as indicate whether you're at risk for weight-related diseases.
Description
Your BMI measurement is calculated by dividing your weight in kilograms by your height in meters squared. Alternatively, you can find your BMI by dividing your weight in pounds by your height in inches squared, and then multiplying the result by 703. In general, a BMI between 18.5 and 24.9 is considered healthy, 25 to 29.9 is overweight, 30 and above is obese and below 18.5 is underweight. The World Health Organization divides these classifications further by labeling a BMI of 30 to 34.99 as obese class I, 35 to 39.99 as obese class II and above 40 as obese class III, while a BMI of 17 to 18.49 is labeled mild thinness, 16 to 16.99 is moderate thinness and below 16 is severe thinness.
Function
Your BMI can serve as an indirect measure of your body fat, helping you assess your risk of weight-related diseases. As the Centers for Disease Control and Prevention explains, a high BMI can indicate increased risk for conditions such as hypertension, type 2 diabetes, stroke, gallbladder disease, sleep apnea, respiratory problems, stroke, high LDL cholesterol, low HDL cholesterol, high triglycerides, osteoarthritis and cancers such as endometrial, breast and colon. Because your BMI is fast and inexpensive to measure, it can serve as a useful alternative to more invasive and costly body fat measurements.
Accuracy
Although the BMI measurement accurately reflects body fat for most people, BMI can vary based on age, gender and ethnicity, and can be unreliable for some individuals. Women tend to have higher body fat than men even when their BMI measurement is equal, and elderly individuals generally have higher body fat than young people with the same BMI. Likewise, athletes and other highly muscular individuals may be classified as overweight or obese based on their BMI measurement, despite having very low levels of body fat.
Alternatives
Because the BMI scale can only estimate your level of body fat, alternative measurements might be necessary to determine whether your weight is healthy or not, particularly if you carry more muscle than most people. The Centers for Disease Control and Prevention lists underwater weighing, skinfold thickness measurements, isotope dilution, dual-energy x-ray absorptiometry and bioelectrical impedance as more precise ways to determine how much body fat you have.
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