Body Mass Index (BMI) Defined

What Is Body Mass Index?
Some critics argue that the measurement is flawed and has limited use. Rather, if you have a high or low BMI, your physician may have you undergo additional health screenings, such as for waist circumference, high cholesterol, or high blood pressure.
How Do You Calculate BMI?
If math isn’t your strong suit, you can opt to use the CDC’s BMI calculator to figure out your BMI.
To calculate your own number, take your weight in kilograms (kg) divided by the square of your height in meters (m). You can also use your height in inches squared, divide that by your weight in pounds, and multiply by 703.
For example, for a woman who is 140 pounds and 63 inches tall, we can calculate her BMI this way:
- Height in inches squared: 63 x 63 = 3,969
- Weight divided by height squared: 140/3,969 = .03527
- .03527 x 703 = 24.79 BMI
What Is a Healthy BMI?
Here’s what your number means, per the CDC:
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 and over: obese
Although the BMI cutoffs are the same regardless of fitness and age, there are some differences in body composition that BMI doesn’t account for. The older we are, the more fat we carry on our bodies, which weighs less than an athletic body with denser muscle mass.
BMI Chart
BMI in Children and Teens
Instead of following BMI ranges for adults, doctors screen children, adolescents, and teenagers for obesity using what’s called growth chart percentages, which use percentiles. Percentiles represent a child’s BMI relative to other U.S. children who are the same sex and age. This approach can help your doctor understand your child’s body weight and health risks as their bodies continue to grow and develop.
Health Risks of Having a High Body Mass
- Type 2 diabetes
- Heart disease
- High blood pressure
- Osteoarthritis
- Gallstones
- Breathing problems
- Certain cancers
This phenomenon, as noted in some studies, is called the “obesity paradox” and may be partially explained by the fact that extra weight and muscle can minimize the metabolic consequences of some diseases. The researchers noted, however, the shortcomings of BMI and proposed that future research should consider body composition when defining obesity rather than simply BMI, to better understand this paradox.
Risk Factors for a High BMI
How to Lower BMI
Losing weight is hard — and keeping it off can be even harder. Most people put on weight over a long period of time, so lowering your BMI may take a while as well. Gradual, practical changes to your lifestyle can ultimately lead to long-lasting results. If you need additional help, reach out to your primary care doctor or find help from a nutritionist skilled in weight loss support.
Make Smart Food Choices
Several healthy diet plans are at your disposal to help you take off extra pounds. But in general, eating more low-calorie, high-fiber foods such as nonstarchy vegetables, fruits, beans, and whole grains — and less fatty and processed food — is a tried-and-true way to lower your body weight.
Exercise Regularly
Get Adequate Sleep
Manage Stress Well
Why BMI Isn’t Perfect: What to Know About the Calculation’s Flaws
BMI paints a picture of only a portion of a person’s health. Although BMI takes your weight and height into account, it doesn’t consider other factors that are known to affect disease risk, such as high blood pressure, blood sugar, and cholesterol.
“There is not just one data point” when it comes to assessing someone’s health risks, says Janice Baker, RDN, CDCES, a registered dietitian and certified diabetes educator in San Diego. She adds that it’s important for physicians to assess factors like muscle mass, activity level, and nutrition when determining how healthy or unhealthy a person is.
- Weight-to-height ratio
- Waist circumference
- Waist-to-hip ratio
- Skinfold thickness
- Bioelectric impedance
- Underwater weighing
- Being an athlete
- Being pregnant
- Being elderly
- Being nonwhite
The Takeaway
- Body mass index is a measure of your weight in relation to your height. Healthcare professionals have long used this number to determine if someone has underweight, healthy weight, overweight, or obesity.
- Online calculators can help you determine your BMI. A number below 18.5 is considered underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or over is obese.
- BMI should be viewed as a simple measurement that can help doctors identify potential concerns, but it doesn’t definitively account for whether a person’s weight will cause health problems.
- You can lower your BMI by making smarter food choices, exercising regularly, and managing stress, and getting enough sleep.
Common Questions & Answers

Justin Laube, MD
Medical Reviewer
Justin Laube, MD, is a board-certified integrative and internal medicine physician, a teacher, and a consultant with extensive expertise in integrative health, medical education, and trauma healing.
He graduated with a bachelor's in biology from the University of Wisconsin and a medical degree from the University of Minnesota Medical School. During medical school, he completed a graduate certificate in integrative therapies and healing practices through the Earl E. Bakken Center for Spirituality & Healing. He completed his three-year residency training in internal medicine at the University of California in Los Angeles on the primary care track and a two-year fellowship in integrative East-West primary care at the UCLA Health Center for East-West Medicine.
He is currently taking a multiyear personal and professional sabbatical to explore the relationship between childhood trauma, disease, and the processes of healing. He is developing a clinical practice for patients with complex trauma, as well as for others going through significant life transitions. He is working on a book distilling the insights from his sabbatical, teaching, and leading retreats on trauma, integrative health, mindfulness, and well-being for health professionals, students, and the community.
Previously, Dr. Laube was an assistant clinical professor at the UCLA Health Center for East-West Medicine and the David Geffen School of Medicine at UCLA, where he provided primary care and integrative East-West medical consultations. As part of the faculty, he completed a medical education fellowship and received a certificate in innovation in curriculum design and evaluation. He was the fellowship director at the Center for East-West Medicine and led courses for physician fellows, residents, and medical students.

Angela Lemond, RDN
Author
Angela Lemond left a successful career in corporate marketing to become a registered dietitian nutritionist practitioner at Lemond Nutrition. She has catapulted up the ranks like a rocket as a national influencer in wellness, family nutrition, behavioral health, and digestive nutrition. Quoted in thousands of articles as a nutrition authority, she now finds interest in setting the record straight through her writing. She owns Lemond Nutrition, a multi-location private practice based in Plano, Texas. Apart from writing for Everyday Health, she has written for various websites and publications such as Consumer Health Digest, EatRight, EatRightTexas and Dallas News Moms Blog.

Cathy Garrard
Author
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