What is BMI (body mass index)?

BMI is a measure of a person's body weight in relation to their height. In this video, bariatric surgeon Neil McDevitt, MD, of Trident Medical Center explains the ranges of BMI and what each means to your overall health.
BMI (body mass index) is a calculation based on a person's height and weight. A BMI between 18.5 and 24.9 is considered healthy weight. Someone with a BMI in the 25 to 29.9 range is considered overweight, and a BMI over 30 qualifies a person as obese.
Denise M. Dietz, MD
Cardiology (Cardiovascular Disease)
Body mass index (BMI) is a calculated, numerical value of your weight in relation to your height. A BMI of less than 18.5 kg/m² is considered underweight. A BMI between 18.5 and 25 kg/m² indicates a normal weight. A BMI between 25 kg/m² and 29.9 kg/m² is considered overweight. A BMI of 30 kg/m² or higher is considered obese. This should be a no brainer, as the Center for Disease Control (CDC) states that overweight and obese people have an increased risk of suffering from heart disease, stroke, some cancers, type 2 diabetes, joint problems, chronic inflammation and various other health conditions. Exercise and a healthy weight also lends itself to higher confidence and lower incidence of depression, which together lead to improved health.
Your BMI is your height to your weight. Body Mass Index is measured on a number scale and being between 18.5 and 24.9 is considered to be a normal weight range. Anything below 18.4 is considered underweight and anything above 25 is considered obese.
Marjorie Nolan Cohn
Nutrition & Dietetics
Overweight and obesity are both labels for ranges of weight that are greater than what is generally considered healthy for a person’s height. The terms overweight and obese also identify ranges of weight that have been shown to increase the likelihood of certain diseases and other health problems.

For adults, overweight and obesity ranges are determined by using weight and height to calculate a number called the "body mass index" (BMI). BMI is used because, for most people, it correlates with their amount of body fat.

It is important to remember that although BMI correlates with the amount of body fat, BMI does not directly measure body fat. As a result, some people, such as athletes, may have a BMI that identifies them as overweight even though they do not have excess body fat. For more information about BMI, visit Body Mass Index.
Eric Beard
Sports Medicine
Body Mass Index (BMI) is a number calculated from the relationship between a person's weight and height. A BMI number or "score" places individuals in weight categories. These categories can range from severely underweight to morbidly obese. Having a low BMI can place someone at risk for the following health conditions and diseases; osteoporosis, impaired immune system function, amenorrhea, cardiac abnormalities and more. Obesity and morbid obesity, or having a high BMI score are risk factors for blood (fat) lipid abnormalities, cancer, including cancer of the uterus, cervix, ovaries, breast, colon, rectum and prostate, depression, gallbladder disease, gynecological problems, such as infertility and irregular periods, heart disease, high blood pressure, metabolic syndrome, nonalcoholic fatty liver disease, osteoarthritis, skin problems, such as intertrigo and impaired wound healing, sleep apnea, stroke, type 2 diabetes according to the Mayo Clinic.
 
Below 18.5 = Underweight
18.5 – 24.9 = Normal
25.0 – 29.9 = Overweight
30.0 and Above = Obese
Anthony L. Komaroff, MD
Internal Medicine
The body mass index (BMI) is an index of weight by height. You can calculate your BMI like this: divide your weight in pounds by your height in inches. Divide the answer by your height in inches. Multiply that answer by 703. Or use the National Heart, Lung, and Blood Institute's easy online calculator. [http://www.nhlbisupport.com/bmi/]

The definitions of normal, overweight, and obese were established after researchers examined the BMIs of millions of people and correlated them with rates of illness and death. These studies identified the normal BMI range as that associated with the lowest rates of illness and death.
Dr. Robin Miller, MD
Internal Medicine
The body mass index is a number that is calculated from an equation that uses height and weight. The number gives an indicator of how fat or thin a person is. A body mass index of less than 18.5 is underweight, between 18.5 and 24.9 is a healthy BMI. Twenty-five to 29.9 is an indicator of being overweight. Thirty and above is considered to be obese. The higher BMI’s are associated with increasing risk of heart disease, stroke, high blood pressure, elevated cholesterol, diabetes, gall bladder disease and cancer.
The body mass index (BMI) is a special measurement used to determine whether your weight is healthy for your height. There are five classifications of BMI: Underweight (below 18.5), healthy (18.5-24.9), overweight (25.0-29.9), obese (30.0-39.9), and morbidly obese (more than 40). Knowing your BMI is important, because being overweight puts strain on your heart and can lead to serious health problems.
Ideal Weight Calculator (Body Mass Index) is a reliable indicator of your body’s fitness level, and most importantly, your health risk. It works by representing the relationship between your weight and height to your body fat level.

To get your BMI, go to http://www.weight-loss-plans-4-you.com/ideal-weight-calculator.html.
Harris H. McIlwain, MD
Rheumatology
Some research shows that the Body Mass Index (BMI) may be the best indicator of a healthy -- or unhealthy -- weight. Your BMI represents the relationship between weight and height and correlates with body fat. For adults aged 20 years or older, the BMI falls into one of these categories:
  • underweight
  • normal
  • overweight
  • obese
Diet for a Pain-Free Life: A Revolutionary Plan to Lose Weight, Stop Pain, Sleep Better and Feel Great in 21 Days, ADA...sound nutritional advice...do-able, delicious..a godsend to pain sufferers.

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Diet for a Pain-Free Life: A Revolutionary Plan to Lose Weight, Stop Pain, Sleep Better and Feel Great in 21 Days, ADA...sound nutritional advice...do-able, delicious..a godsend to pain sufferers.

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BMI stands for Body mass Index and is an index of a person's weight in relation to their height. BMI is a common technique used to determine thinness and excessive fatness in the body. Because of its simplicity and consistency, BMI is the most commonly used method in determining overweight and obesity in the general population. It is also commonly used for determining health risks associated with excessive body fat. Research shows that health risks start to increase when the BMI exceeds 25.0 -- which classifies an individual as being overweight.
BMI stands for body mass index. BMI uses height and weight to calculate a number that indicated body fatness. Although BMI does not directly measure body fat, research has shown that BMI does directly correlate to measures that are used to measure body fat percentage (skin caliper, DXA, bioelectrical impedance analysis, etc.). BMI is used in mass to indicate body fatness because it is a simple, inexpensive, and non-invasive screening tool.

BMI for children and teens (ages 2 - 19) is plotted on a gender specific age chart. The chart indicates a percentile ranking relative to other children among the same gender and age. A child is considered to be in the healthy weight category between the 5th and 85th percentile. A child in the overweight category falls between the 85th and 95th percentile and a child with a BMI greater than the 95th percentile categorized as obese. A high BMI has been linked to increased risk factors associated with cardiovascular disease, such as high blood pressure, high cholesterol, and type 2 Diabetes; however, BMI should only be used as part of the screening process. The child’s physician will look at other assessments and health screenings to determine if excess body fat is a concern for that child.
William D. Knopf, MD
Cardiology (Cardiovascular Disease)
BMI stands for body mass index, a measure that relates body weight to height. BMI is sometimes used to measure total body fat and whether a person is a healthy weight. Excess body fat is linked to an increased risk of some diseases including heart disease and some cancers.

This answer is based upon source information from the National Cancer Institute.
Weight Watchers®
Administration
BMI stands for body mass index, and it's a scientifically accepted measurement of body weight as it relates to health. While BMI is not a direct measure of excess body fat, it is the recommended method to diagnose overweight and obesity.

BMI is calculated from a person's weight and height, regardless of gender. To calculate your BMI, divide your weight in pounds by your height in inches squared. Multiply that total by 703. Or, divide your weight in kilograms by your height in meters squared.

A BMI of 20 to 25 is considered the healthiest BMI range for most adults. If your BMI is over 25, you are considered to be in a higher risk category for developing health problems associated with weight.

Weight Watchers can help you reach that healthy range. Learn more about Weight Watchers and how to join.
Dr. Mike Clark, DPT
Fitness
The BMI (Body Mass Index) is a mathematical formula that factors a person’s height and weight in determining obesity. It may be less accurate for athletes or older persons who have lost muscle mass.

BMI, what does it mean?
Weight               BMI
Underweight      Below 18.5
Normal              18.5 - 24.9
Overweight        25.0 - 29.9
Obesity             30.0 and Above

You can use the tool below to calculate your BMI:

http://www.mayoclinic.com/health/bmi-calculator/NU00597
Wendy Batts
Fitness
Body Mass Index (BMI) is a ratio of someone’s height and weight. It is one way to measure body fatness and is widely used because it is easy to perform, inexpensive and doesn’t require any tools and processes other than a calculator and a formula. While it doesn’t directly measure body composition or body fat, it correlates well to the actual fat content of the body and is a reliable measure.

It is used primarily to place someone in a weight category and serve as an additional tool in assessing their risk for chronic diseases related to being overweight and obese.
Rose Reisman
Nutrition & Dietetics
One of the most widely used methods of determining obesity is body mass index, better known as BMI. This standard method evaluates body weight in relation to height. BMI is one way to determine if someone is an ideal weight, overweight or obese. A healthy BMI range is between 19 and 25. A BMI between 25 and 29 is considered moderately overweight, and over 29 indicates obesity.

To find your BMI, multiply your weight in pounds by 705, then divide the result by your height in inches, then divide again by your height. The result is your BMI. Get out your calculator.

For example, a woman weighs 150 pounds and her height is 5 feet 6 inches (66 inches):

150 lb x 705 = 105,750
105,750/66 = 1602
1602/66 = 24 BMI

This woman's BMI is in the healthy range.

Don't take the BMI as the only indicator of healthy or unhealthy weight, since the index makes no allowance for different body builds. The BMI treats a large-framed person in the same way that it treats a small-framed person.
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Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
BMI, which stands for body mass index, has been widely used in the United States to measure obesity since 1985, although it was first used in the 19th century. It was rediscovered in the mid-20th century, when legendary diet  researcher Ancel Keys, PhD, determined that it was the best available obesity measurement. The formula for BMI is the ratio of a person's weight to her height squared, which provides a better measure of body fat than a simple height/weight ratio. No obesity measurement is perfect, and the BMI isn't suited to people who are particularly muscular, for example, but it remains the primary tool for measuring overweight and obesity to this day.
Dawn Marcus
Neurology
Most doctors define overweight and obesity using the body mass index (BMI), which takes into consideration your weight in relation to your height. A normal BMI is less than 25. BMIs between 25 and 29.9 show that you're overweight. If your BMI is 30 or higher, you are obese, meaning you have a serious and unhealthy amount of excess weight. For example, if you are 5 feet 9 inches tall, your healthy weight would be approximately 125-168 pounds. Between 169 and 202 pounds, you'd be considered overweight, and if you weigh over 202 pounds you would be considered obese. BMI calculators on the Internet can calculate this for you.
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Body mass index (BMI) is a calculation you can use to see if you're at a healthy weight. It is the answer to the question: What is my ideal weight? To find your BMI, multiply your weight in pounds by 703. Then square your height in inches. Divide the first number by the second number to calculate your BMI. For example, if you're 112 pounds and 5'4" (64 inches) multiply 112 by 703. Then multiply 64 times 64. Divide the first number (78,736) by the second number (4,096), and you get a BMI of 19.2. A BMI between 19 and 24 is normal weight. A BMI of 25 to 29 is overweight. A BMI over 30 is considered obese.
RealAge
Administration

Body mass index (BMI) measures the relationship (or ratio) of your weight to your height. It is an estimation of body composition based on the notion that your body weight should be proportional to your height.

Lawrence J. Cheskin, MD
Internal Medicine

Body-mass index is a measure of “relative weight,” in other words, how much you weigh relative to your height.  It has essentially supplanted the older Metropolitan Life Insurance weight-height tables of “ideal weight.” The formula for BMI is in metric units: kilograms per meter-squared.

Unlike older tables, BMI does not attempt to adjust ideal weight for frame size. A BMI of less than 18.5 is underweight, 18.5- 24.9 is normal weight, 25-29.9 is overweight, 30-39.9 is obese, and 40+ is severely obese (usually 100+ lbs over ideal weight).

BMI is a mathematical formula that expresses the ratio of your weight to your height. Studies have shown that this ratio is a better predictor of body fat than any other measure of height and weight. All adults with a BMI of 25 or more are considered to be at risk for premature death and disability, and this risk increases as the severity of obesity increases.
Dr. Michael Roizen, MD
Internal Medicine
The customary way to calculate your ideal weight is to determine your body mass index (BMI) or your weight-to-height ratio. Although The BMI is one of the best tools we have for assessing whether or not a person weighs too much it is not very useful in young body builders or athletes. The BMI is useful for the majority of us as it accounts for variances in body size, giving a standard for evaluating people at a range of heights. (BMI does not provide the best possible measure of body fat, for most people BMI provides a good general estimate and can easily be calculated at home.)
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Body mass index (BMI) is a measure of your weight in relation to your height. BMI is an assessment tool for determining whether your weight falls within one of four categories.

People with BMIs under 18.5 are considered underweight. Your weight is said to be within the healthy range if your BMI is 18.5 to 24.9. People with BMIs between 25 to 29.5 are considered overweight, while those whose BMI are above 30 are obese.

Remember, one size does not fit all. Other factors such as body build, age and ethnicity are not considered in this equation.
William B. Salt II., MD
Gastroenterology
The BMI is a reliable indicator of total body fat, which is related to the risk of disease and death. The score is valid for both men and women, but it does have some limits. It may overestimate body fat in athletes and others who have a muscular build. For example, one-half of NBA basketball players have an elevated BMI. Furthermore, it may underestimate body fat in older persons and others who have lost muscle mass. Think of BMI as a range, rather than a fixed number like your shoe size. It is best used as a guideline to determine where you are now and provide a goal of what you should weigh to be in a healthy range, if you are not already there. If you are within the under-twenty-five range, try avoiding gaining weight and remain there, even if you have some extra room above your number.
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Body mass index (BMI) represents the relationship of height to weight, yielding a single number; the more you weigh in relation to your height, the higher your BMI. Using BMI as the measure, “obese” is defined as a body mass index of 30 or higher, and “overweight" as 25-29.9. A desirable BMI is anything less than 25, and the lower the better, to a point.
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Body mass index is a very safe and effective way that will give you a pretty good estimate of your total body fat. The formula simply takes your weight in kilograms and then divides it by your height in metered squares. if you average anything in the range of 25 - 30 that will put you in the category of over weight. Anything above 35 will put you in a zone of obese. Get to know your BMI today.
Tonya Bolden
Alternative & Complementary Medicine

Experts say the old height/weight charts aren’t necessarily the best way to determine whether a person needs to lose or gain weight. Instead, they use as a guide Body Mass Index (BMI), a measure of how much fat you’re packing. If you are curious about your BMI and math is not your strong suit, you can find BMI calculators online.

Here’s what the numbers indicate:

Underweight: Below 18.5

Normal:  18.5–24.9

Overweight:  25.0–29.9

Obese:  30.0 and above

Morbidly Obese:  40.0 and above

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Discovery Health
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Body Mass Index is a mathematical formula that helps determine whether people are at a healthy weight. The calculation of BMI takes into consideration height and body weight to determine whether a person is at a healthy weight, or is underweight or overweight.

For example, a person who's 6'4" and weighs 200 pounds is probably at a healthy weight. But someone who's 5'9" and weighs 200 pounds is probably overweight.

Broadly speaking, the BMI helps officials get a general idea of how weight and obesity affect the population's health. With individuals, it enables a doctor to identify weight problems in a patient before serious health conditions arise.

Studies show that being overweight or obese can greatly increase a person's risk for developing conditions such as heart disease, diabetes, osteoarthritis or some types of cancer.

And being underweight can also lead to greater health risks from malnutrition.

Body mass index, often referred to as BMI, is a measurement designed to assess prevalence of obesity-related diseases. It is important to note that BMI does not assess body fat, it is merely a method to determine whether or not an individual’s weight is appropriate to their height. Therefore, BMI may have a certain degree of error associated with it. For example, if a 200 pound 5’6” bodybuilder with a body fat of 6% calculates their BMI to be a little more than 32 they would appear to be obese. But, clearly the body builder is not battling obesity, the calculation just fails to account for the large amount of muscle. BMI is one of the most widely used measures because there is a minimal amount of user calculation error. Most people can measure height and weight accurately. To determine BMI, take weight (in kilograms) and divide by height (in meters squared). The result of this equation is the individual's BMI. There are three classification ranges of BMI which will determine the risk factor associated with obesity. Mild risk for obesity-related diseases occurs for those with a BMI between 25 and 30. Moderate risk for obesity-related diseases occurs for those with a BMI between 30 and 35. Sever risk for obesity-related diseases occurs for those with a BMI greater than 35.

Continue Learning about Body Mass Index (BMI)

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.