Show Medically reviewed by Natalie Olsen, R.D., L.D., ACSM EP-C — Written by Yvette Brazier on November 9, 2018 Body mass index, or BMI, is a measure of body size. It combines a person’s weight with their height. The results of a BMI measurement can give an idea about whether a person has the correct weight for their height. BMI is a screening tool that can indicate whether a person is underweight or if they have a healthy weight, excess weight, or obesity. If a person’s BMI is outside of the healthy range, their health risks may increase significantly. Carrying too much weight can lead to a variety of health conditions, such as type 2 diabetes, high blood pressure, and cardiovascular problems. A weigh that is too low can increase the risk of malnutrition, osteoporosis, and anemia. The doctor will make suitable recommendations. BMI does not measure body fat directly, and it does not account for age, sex, ethnicity, or muscle mass in adults. However, it uses standard weight status categories that can help doctors to track weight status across populations and identify potential issues in individuals. Share on PinterestA BMI chart or calculator can show a person if they have a healthy weight. Calculating BMI involves measuring a person’s height and body weight. Metric
Since most people measure height in centimeters (cm), divide height in cm by 100 to get height in meters. Imperial
To avoid using the math, a person can use a calculator or a chart to find their BMI. BMI calculatorEnter height or weight in either imperial or metric measurements to find your BMI. BMI chartsPeople can also work out their BMI using a chart. Click here to see a chart provided by the National Heart, Lung, and Blood Institute (NHLBI). Locate your height in inches on the side of the chart, then look across to find your body weight in pounds. Scan to the top to see if the result corresponds to a normal weight, overweight, or obesity. The following table shows standard weight status categories associated with BMI ranges for adults.
BMI of less than 18.5 A BMI of less than 18.5 indicates that you are underweight, so you may need to put on some weight. You are recommended to ask your doctor or a dietitian for advice. BMI of 18.5–24.9 A BMI of 18.5-24.9 indicates that you are at a healthy weight for your height. By maintaining a healthy weight, you lower your risk of developing serious health problems. BMI of 25–29.9 A BMI of 25-29.9 indicates that you are slightly overweight. You may be advised to lose some weight for health reasons. You are recommended to talk to your doctor or a dietitian for advice. BMI of over 30 A BMI of over 30 indicates that you are heavily overweight. Your health may be at risk if you do not lose weight. You are recommended to talk to your doctor or a dietitian for advice. In adults, BMI values are not linked to age and are the same for both sexes. However, measuring BMI in children and teens is slightly different. Girls and boys develop at different rates and have different amounts of body fat at different ages. For this reason, BMI measurements during childhood and adolescence take age and sex into consideration. Doctors and other health professionals do not categorize children by healthy weight ranges because:
Doctors calculate BMI for children and teens in the same way as they do for adults, by measuring height and weight. Then they locate the BMI number and person’s age on a sex-specific BMI-for-age chart. This will indicate whether the child is within a healthy range. Calculator and charts for child and teen BMIThe Centers for Disease Control and Prevention (CDC) have produced a calculator that provides BMI and the corresponding BMI-for-age percentile on a CDC growth chart for children and teens. First, click here for the calculator. Next, use the charts to see if a child’s weight is suitable for their age. Click here for the charts:
What do the results mean?The following categories explain the meaning of the results:
BMI is not accurate enough to use as a diagnostic tool, but it can screen for potential weight problems in adults and children. If someone has a high or low BMI, a doctor or other healthcare professional might then consider other factors, such as:
The doctor or healthcare professional can then make diet and exercise recommendations based on these results. Excess weight has the following effects on the body:
According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), carrying extra weight can increase the risk of the following conditions:
Carrying extra weight as a child or teenager can also pose significant health risks, both during childhood and into adulthood. As with adult obesity, childhood obesity increases the risk of various health problems, including cardiovascular disease, diabetes, and sleep apnea. The American Heart Association (AHA), point out that children with a high BMI also have a higher risk of:
Benefits of a healthy weightShare on PinterestWalking with family or friends can be an enjoyable way of keeping fit and preventing unwanted weight gain. Apart from reducing the risk of the health conditions, maintaining a healthy weight offers additional benefits:
BMI is a useful tool, but it cannot identify whether a person’s weight is made up of muscle or fat. For example, an athlete with a lot of muscle tissue may have a higher BMI than a person who is not very active. But, this does not mean that the athlete is overweight or unhealthy. In addition, cardiovascular disease and high blood pressure are more likely to occur in people who have additional fat — known as visceral fat — around their middle rather than their hips. Other measures of body size include waist-hip ratio, waist-to-height ratio, and body composition, which measures body fat and lean body mass. These measurement systems focus more on the amount of fat a person has and its distribution around the body. Together with BMI, these additional measures can help to assess more accurately the health risks associated with an individual’s weight. BMI can be a useful screening tool for predicting certain health risks. However, people should use it with caution, as it does not take other factors — such as activity levels and body composition — into account. For children and teens, it is important to include their age and sex when taking a BMI measurement, because their bodies continuously change as they develop. Last medically reviewed on November 9, 2018
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