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Body Mass Index (BMI) Calculator

While we Canadians are supersizing our meals, we're also supersizing ourselves. More than 40 percent of adults in Canada are overweight or obese, creating many health problems, including an increased risk of heart disease, stroke, diabetes, high blood pressure, arthritis, varicose veins, and even some types of cancer.

BMI: An Indicator of Weight Status

The body mass index (BMI) is a quick and easy way to see if your weight is within the normal or average range for your height. It might sound complicated, but your BMI is just a calculation using the ratio of your weight to your height to determine how much body fat you have. It was originally developed in the 19th century by a well-known statistician, Lambert Quetelet, but has undergone changes over the years as scientists learn more about the relationship between weight and health.

Ken Fujioka, MD, director of the Center for Weight Management and director of nutrition and metabolic research at Scripps Clinic in La Jolla, Calif., says that knowing your BMI can be particularly helpful if you are between 20 and 30 pounds overweight. “Most Americans can tell if they are overweight by stepping on the scale," Dr. Fujioka says. And if someone is seriously overweight, they know it. But if your weight is borderline between normal and overweight, checking your BMI can be useful.

BMI: Calculating Your Number

There are three easy ways to find out your BMI using your height and weight:

1. Use My Calorie Counters BMI Calculator, which computes your BMI after you enter your height and weight.

2. Use a table, like the one at the National Heart, Lung and Blood Institute Web site.

3. Calculate the BMI yourself in three steps:

Step 1: Multiply your weight by 703.
Step 2: Divide that number by your height in inches.
Step 3: Divide that number again by your height in inches.

Here's an example using a man who weighs 165 pounds and is 6'2, or 74", tall:

Step 1: 165 x 703 = 115,995
Step 2: 115,995/74 = 1,567.5
Step 3: 1,567.5/74 = 21.18

His BMI is 21.

BMI: Healthy Range

Once you have your BMI, find out where you fit in the BMI range. The BMI ranges indicate whether a person is underweight, normal weight, overweight (weighing more than a healthy amount), obese (more overweight), or morbidly (dangerously) obese.

If your BMI is less than 18.5, you are underweight.
If your BMI is between 18.5 and 24.9, you are normal weight.
If your BMI is between 25 and 29.9, you are overweight.
If your BMI is between 30 and 39.9, you are obese (more overweight).
If your BMI is 40 or over, you are dangerously obese.

With a BMI of 21, the man in our example is at a normal weight.

Note that the BMI ranges for children are different, and it's important to ask your child's doctor about the BMI for their age.

If you fall into any category other than normal weight, even "underweight", it's time to talk to your doctor about improving your eating habits to reach a healthy weight, whether that is by counting calories, changing the content of your diet, or trying another weight control method.

While most people with BMI in the overweight, obese, or morbidly obese ranges have extra body fat, there are exceptions. Some athletes, such as bodybuilders, are actually heavy because of their muscle mass, not body fat. So the meaning of BMI may be different for those people.

BMI is an important way to determine whether you have excess fat which could lead to health problems, but it is not the only way. Your waist circumference, which is linked to abdominal fat, is another useful measurement. Men with a waist circumference of 40 inches or more are more likely, in general, to develop risk factors for heart disease and other health problems; for women, that number is 35 inches. Other risk factors for heart disease are diabetes, high blood pressure, smoking, physical activity, and family history.

If your BMI is too high, don't despair. "We know much more about weight loss now than ever before, and we have more tools to help people reach their goal," Fujioka says.

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