What is a BMI? - PIH Health

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Published on April 03, 2017

What is a BMI?

BMI Calculation

BMI CalculationBody-Mass-Index: A Simple Definition

Your BMI is a number that is calculated using a very simple formula, which considers your weight in relation to height. Many health professionals use this information to talk to their patients about their weight and its connection to health.

How Do I Calculate BMI?

An individual’s BMI is calculated by dividing their weight in kilograms by his or her height (squared).  If you want to skip the math and just get your number, there are plenty of online BMI calculators that can do the work for you.

What Does My Body-Mass-Index Really Mean?

Once you have determined your BMI, you can use this number to identify your corresponding weight category. These categories are as follows:

  • Underweight – BMI <18.5
  • Normal – BMI 18.5 – 24.9
  • Overweight – BMI 25 – 25.9
  • Class 1 Obesity – BMI 30 – 34.9
  • Class 2 Obesity – BMI 35 - 39.9
  • Class 3 Obesity – BMI > 40

Although these numbers are helpful, you should also be aware that they are not a definitive representation of your overall health and weight category. Because the number is developed through such a simple formula, it doesn’t take into account factors such as body frame and body composition. For example, a body builder could have a BMI that is greater than 30, but does not indicate obesity

If My BMI isn’t Always Accurate, Why is it Used?

BMI is a useful tool because we can use this number as a starting point. Your BMI can provide a general indication of your weight category, and it can give you an idea for what kind of goals to set for your overall weight and health.  It is well established that health risk factors are lowered if a person maintains a BMI of less than 25.

Some other helpful ways to assess and analyze your weight include:

  • Tracking changes on a scale once a week or even twice a month
  • Paying attention to your body and how you’re feeling physically
  • Observing changes in the way your clothes fit
  • Making regular visits to see your doctor and monitor your health

The information in Healthy Living Online is for educational purposes only.  It is not intended nor implied to be a substitute for professional medical advice.  The reader should always consult his or her healthcare provider to determine the appropriateness of the information for their own situation, or if they have any questions regarding a medical condition or treatment plan.

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