Body Weight and Cancer Risk

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Normal weight ranges: Body mass index (BMI)

Body mass index, or BMI, is a way to help you figure out if you are at a healthy weight for your height. 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. The same groups apply to both men and women.

  • 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

What is my BMI?

There are several ways to find your BMI.

Charts and online calculators

Charts and tables, such as the one below, are one easy way to figure out your BMI. There are also several online BMI calculators, such as this one on our website.

To use the table below, find your height on the left side of the chart, then go across to the weight that is closest to yours. At the top of the chart you can see your BMI, and at the bottom of the chart you can see which category you fit into – healthy weight, overweight, or obese:

Some examples

This table shows us that a woman who is 5 ft. 4 in. tall is considered overweight (BMI is 25 to 29) if she weighs between 145 and 169 pounds. She is considered obese (BMI is 30 or more) if she weighs 174 pounds or more.

A man who is 5 ft. 10 in. tall is considered overweight (BMI is 25 to 29) if he weighs between 174 and 202 pounds, and is obese (BMI is 30 or more) if he weighs 209 pounds or more.

Calculating my BMI

You can also calculate your own BMI. The actual formula to determine BMI uses metric system measurements: weight in kilograms (kg) divided by height in meters, squared (m2).

When using pounds and inches, the formula needs to be altered slightly. Multiply your weight in pounds by 703. Divide that by your height in inches, squared:

BMI = (your weight in pounds x 703) ÷ (your height in inches x your height in inches)

For example, if you weigh 120 pounds and are 5 ft. 3 in. (63 in.) tall:

BMI = (120 x 703) ÷ (63 x 63) or 84,360 ÷ 3969 = 21.3

This is well within the healthy weight range.

Are there any problems using the 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.

BMI in children and teens

BMI can be calculated the same way for children and teens as it is for adults, but the numbers don’t have the same meaning. This is because the normal amount of body fat changes with age in children and teens, and is different between boys and girls. So for kids, BMI levels that define being normal weight or overweight are based on the child’s age and gender.

To account for this, the US Centers for Disease Control and Prevention (CDC) has developed age- and gender-specific growth charts. These charts are used to translate a BMI number into a percentile based on a child’s sex and age. The percentiles are then used to determine the different weight groups:

  • Underweight: less than the 5th percentile
  • Normal weight: 5th percentile to less than the 85th percentile
  • Overweight: 85th percentile to less than the 95th percentile
  • Obese: 95th percentile or higher

An easy way to determine your child’s BMI percentile is to use the CDC’s online BMI percentile calculator at http://apps.nccd.cdc.gov/dnpabmi.

Even in a young person, being overweight or obese can cause health problems. And it may directly increase the risk for certain health problems later in life, including some kinds of cancer. It also increases the chances of being overweight or obese as an adult, as well as the risk of health problems that can come with this.


Last Medical Review: 04/24/2015
Last Revised: 04/24/2015