What's Your BMI and What Does it Mean?

Woman weighing herself on scale
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Body Mass Index or BMI is a calculation that determines weight status in adults by using your weight and height. The end result tells you if you're underweight, at a healthy weight, overweight or obese. A body mass index:

  • Over 40 is considered morbidly obese.
  • Over 30 is considered obese.
  • Between 25 and 29.9 is considered overweight.
  • Between 18.5 and 24.9 is considered a healthy bmi.
  • Under 18.5 is consider underweight.

    Calculate Your BMI

    One option to calculate your BMI is to use an online BMI Calculator.  You can also use this formula, which is pretty simple to follow, even for math idiots like myself:

    BMI = ( Weight in Pounds / (Height in inches x Height in inches ) ) x 703

    That means you divide your weight in pounds (lbs) by height in inches (in) squared and then multiply by a conversion factor of 703.

    So, let's say we're calculating the BMI of someone who's 5'5" and weighs 156 pounds.  Here's what that calculation looks like:

    BMI = 165/(4225) x 703

    BMI = 27.5

    The Drawbacks of Using BMI

    The BMI formula is so simple, it's easy to use by just about everyone.  However, it's that simplicity that makes it inaccurate because it only takes into account your height and weight.  Whether you're overweight or not requires much more information than just your height and weight.

    Here are all the things that this BMI formula can get wrong:

    • How much muscle you have - The more you have the higher your BMI will be, even though you may be healthy
    • Frame size - A person with a big frame will have a higher BMI, although he or she may still be healthy
    • Gender - At the same BMI, women will usually have more body fat than men
    • Age - At the same BMI, an older person will usually have more fat than younger adults
    • If you're an athlete - At the same BMI, athletes will usually have less body fat than people who aren't athletes.

    That means if you're very muscular, pregnant or have a large frame, your BMI calculation may show you as overweight or obese, even when you're not.

    How your body fat is distributed is also important for predicting your risk of heart disease, obesity-related illnesses and death. It's a good idea to use a variety of tools to determine how healthy your weight and body fat is including waist-to-hip ratio and/or your body fat percentage.

    Is BMI on it's Way Out?

    What's interesting now is that new research, published in the International Journal of Obesity, suggests BMI is seriously flawed.  This study revealed that millions of Americans are labeled as overweight or obese, based on their BMI, but are perfectly healthy.

    The findings suggest that about 34.4 million Americans are considered overweight based on BMI and that 19.8 million are considered obese.  Which is just crazy!

    So, What's Wrong With BMI? 

    As I mentioned above, BMI doesn't take into account all of the factors that make us healthy.

    What's even more disturbing is that many companies in the U.S. use employees' BMI as a factor in determining their health care costs.  So, a person with a high BMI may pay higher premiums, even though it isn't clear whether that person is genuinely overweight and unhealthy or not.

    There's definitely a call to get rid of BMI as a way to measure health and weight and, because of this study, we may just see that happen.  Good riddance.


    Tomiyama, AJ, JM Hunger, and J. Nguyen-Cuu. "Misclassification of Cardiometabolic Health When Using Body Mass Index Categories in NHANES 2005–2012." International Journal of Obesity (2016). Doi: 10.1038/ijo.2016.17. Web. 02 Feb. 09.

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