Since a typical scale only measures your total weight, it helps to have more information to determine if that weight is healthy or unhealthy. A person who is six feet tall and weighs 198 pounds is probably going to have a smaller amount of body fat than a person who is five feet tall and 198 pounds. The BMI combines your weight and your height into a score that helps you determine if you are underweight, at a healthy weight, overweight, or obese.
BMI is calculated with the following formula:
weight (lb) / [height (in)]2 x 703
or in metric:
weight (kg) / [height (m)]2
You can use a BMI calculator to do the math for you.
You can compare your BMI to this table to help you determine whether you're at a healthy weight.
- Underweight = less than 18.5
- Normal weight = 18.5-24.9
- Overweight = 25-29.9
- Obese = 30 or greater
If you are planning to lose or gain weight, you can use your BMI to monitor your progress. It's important to know that your BMI is not the same as your body fat percentage, which is a different number and doesn't correspond to these charts.
People who have a BMI in the overweight or obese ranges may have a higher risk of cardiovascular disease, diabetes, arthritis, and some forms of cancer. However, it's important to see your health care provider, who can take other lifestyle and risk factors into consideration.
The BMI isn't perfect because it's an indirect measurement of fat, and really doesn't differentiate pounds of fat from pounds of muscle and bone. So it doesn't work well for very muscular people or for people who have lost a lot of muscle mass. For example, an elite athlete with a very small amount of body fat will still have a high BMI, and an elderly person may have a lower BMI because they have less muscle mass. In these cases, a better method of measurement is the body fat percentage.
Sources:
Centers for Disease Control and Prevention. "About BMI for Adults." http://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
