BMI stands for body mass index. Your height and weight are used to calculate your BMI. For most people, BMI can be used as an indicator of body fatness. Both the National Institutes of Health (NIH) and The World Health Organization use it as a way to help define overweightness and obesity.
Knowing your BMI is important. For example, if your BMI is too high, you may be at an increased risk for many chronic health problems. These include high blood pressure, type 2 diabetes, coronary heart disease, stroke, gallbladder disease and osteoarthritis. It may also raise your risk for endometrial, breast and colon cancers.
Making sense of the numbers
BMI = [Weight in pounds ÷ Height in inches ÷ Height in inches] x 703. For example, the BMI of a person who is 6 feet tall and who weighs 210 pounds would be: 210 pounds divided by 72 inches, divided again by 72 inches and multiplied by 703 = 28.5.
According to the NIH, your BMI means the following:
- Underweight: below 18.5
- Normal: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obese: 30 and above
Note that it is possible to have a higher BMI but very little fat. Bodybuilders and highly-trained athletes may fall into that category. But most people who are overweight have too much body fat. BMI also may not be accurate for older people and those who have lost muscle. For these groups, BMI may underestimate their amount of body fat.
Overweight children are more likely to be overweight adults. To fight the rising obesity rate among children, the Centers for Disease Control and Prevention have also published BMI charts for children.
Children's BMI charts help doctors identify potential weight problems at an early age. Even though BMI for children and teenagers is calculated the same way as for an adult, the way it is interpreted is different.
For children and teens, interpretation of BMI takes into account both age and sex. That is because body fat for children changes with age. Boys and girls also differ in the amount of body fat they have. BMI in children and teens is reported as percentiles compared with other children of the same sex and age.
Besides knowing your BMI, waist circumference (WC) is a helpful screening measure for certain health risks associated with being overweight or obese. Carrying weight around your middle, rather than on your hips and thighs, puts you at higher risk of heart disease and type 2 diabetes.
The risk goes up for women with a waist of greater than 35 inches around. It goes up for men with a waist greater than 40 inches. For an accurate WC reading, stand, place a tape measure around your middle just above your hip bones and measure after you breathe out.
Toward a healthier BMI
To keep weight off and improve your BMI if you're overweight or obese, you need to reduce your calories and increase your physical activity.
Here are some tips for losing weight and keeping it off.
- Talk to your doctor before you start any weight-loss program. Be wary of fad diets and rapid weight-loss programs. They may give you dramatic short-term results, but may not be effective or may be dangerous in the long term. If you don't get enough calories, your body can go into starvation mode, your metabolism can slow down and weight loss will be even harder.
- Be active. If you don't have much time for exercise, try to give up something else. If you haven't been active, doing too much too soon can lead to burnout and injuries. Talk to your doctor about starting an exercise program that is right for you. You may want to start by walking for 10 minutes a day and gradually build up your time.
- Set realistic weight-loss goals, such as no more than 1/2 to 2 pounds a week. Even a small amount of weight loss can make a huge difference to your health.
- Know what you're eating. Read food labels and pay attention to portion sizes, fat, sugar and sodium content.
- Track your eating and exercising habits by recording them in a diary.
- Stick with it. Don't give up just because you reached a plateau or binged on potato salad at yesterday's barbecue.
Created on 06/20/2000
Updated on 02/26/2013
- Weight-control Information Network. Weight-loss and nutrition myths.
- United States Department of Agriculture. Dietary Guidelines for Americans, 2010.
- Centers for Disease Control and Prevention. About BMI for children and teens.
- National Heart, Lung, and Blood Institute. Aim for a healthy weight: Assessing your weight and health risk.