Find Your Body Mass Index (BMI)
Finding your body mass index, or BMI, is one way to help you figure out if you are at a healthy weight. BMI is a number based on height and weight. It can be used to place a person in categories ranging from underweight to obese.
What is body mass index (BMI)?
Body mass index, or BMI, is one way to look at whether a person is at a healthy weight. BMI is a number based on your weight and height. In general, the higher the number, the more body fat a person has. BMI is often used as a screening tool to decide if your weight might be putting you at risk for health problems such as heart disease, diabetes, and cancer.
BMI is used to broadly define different weight groups in adults 20 years old or older.
- Underweight: BMI is less than 18.5
- Normal weight: BMI is 18.5 to 24.9
- Overweight: BMI is 25 to 29.9
- Obese: BMI is 30 or more
In adults, BMI is calculated the same way for both men and women. There are several ways to find your BMI. (See below for information about how to calculate BMI in children and teens.)
Limitations and concerns about the use of BMI
Doctors and nurses often use BMI to help find out if a person might have a weight problem. BMI gives a good estimate of total body fat for most people, but it doesn’t work well for everybody. For example:
- Bodybuilders or other very muscular people can have a high BMI because of their muscle mass, even though they’re not necessarily overweight.
- The BMI can also underestimate body fat in people who have lost muscle mass, such as some older people.
For most adults, the BMI is a good way to get an idea of healthy weight ranges. But it’s not always the final word in deciding if a person is overweight or obese. There are other things to think about when judging how much someone should weigh.
A person with a high BMI should be evaluated by a health care provider, who might use other factors such as skinfold thickness (a measure of body fat), waist size, evaluations of diet and family health problems, and other factors to find out if a person’s weight might pose a health risk.
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The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.
Last Revised: March 5, 2024
American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.
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