Judgments about body weight can easily become clouded by emotionalism. It’s good to be passionate about managing your body, but you need to get a good grounding in facts, first. BMI is an important tool for achieving that goal.

BMI factors in not only your weight, but also your height. Simply divide your weight in kilograms (1 lb = 0.454 kg) by the square of your height in meters. (1 inch = 2.54 cm)

So, for a person 5 ft 7 in (67 inches) tall, who weighs 120 lbs the calculation would look like this:

Height: 67 inches x 2.54 cm/inch = 170.18 cm = 1.7018 m
Height squared: 1.7018 m x 1.7018 m = 2.896 m^2
Weight: 120 lbs x 0.454 kg/lb = 54.48 kg

So, BMI = 54.48 kg / 2.896 m^2  = 18.81

But what does this number mean? The following table lists one commonly accepted classification, using BMI:

Under 18.5 = Underweight
Between 18.5 and 24.99 = Normal
Between 25 and 29.99 = Overweight
Between 30 and 34.99 = Obese (Class 1)
Between 35 and 39.99 = Obese (Class 2)
40 and above = Extreme Obesity

Of course, anyone near the borderline of one classification shouldn’t panic, since these can’t be anything but guidelines. Nevertheless, anyone nearer the higher range should consider the health risks associated with a high BMI. Some of those are: hypertension, increased risk of cardiovascular disease (heart problems) and increased chance of diabetes. Consult a physician for details.

There are limitations on the usefulness of BMI. It doesn’t take into account different body types, athletic conditioning, age, muscle-to-fat ratio and other characteristics. As a result, it can overestimate the risk for stocky athletes and underestimate it for older individuals who have reduced muscle mass. And, gender isn’t taken into account either. Yet women, just as one example, have a naturally larger percentage of body fat than men, on average.

Another measure is useful to couple with BMI: waist circumference. Since, for men and women both (though particularly for men) body fat is stored preferentially around the waist this can be a useful piece of information. For most men around, say, 5 ft 9 inches a waist measurement over 37 inches (94 cm) is substantial, while one over 40 inches (101.6 cm) indicates a health risk. For women approximately 5 ft 7 inches tall, the numbers are 31 inches (78.7 cm) and 35 inches (89 cm), respectively.

Keep in mind that these are averages, but those with substantial waistlines can see the amount of excess fat stored, confirming that the numbers constitute a useful piece of information.

What to do with, or about, those numbers is a different story, of course. No single measurement tells the whole story about weight, body fat and how to manage it. But these represent useful and objective measures when considering any weight loss program.

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2. The Best Definition Of Obesity Is A Body Mass Index Of Thirty Or More
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There are calculators that you can use online to calculate your BMI for you; all you have to know is that the result is a relationship between your height and your weight.  What you then have to do is interpret your BMI.  The current distinctions between being overweight and being obese are set for adults at 25 and 30, respectively.  What this means is that if your BMI is 24, you are not overweight, but if your BMI is 26, you are considered to be overweight.  If your BMI is 31, you are considered to be obese.  Of course, the fact that the BMI system is numerical means that your BMI falls on a continuum, thus, one person with a BMI of 26 is considered to be less overweight than another overweight person with a BMI of 29.  If your BMI is under 18.5, you are considered to be underweight.

An important thing to take into consideration when calculating and interpreting your BMI is that the percentage of fat and muscle are not taken into account.  As you may know, muscle weighs significantly more than fat does.  What this means is that if your percentage of body fat is very high, then your BMI might be within the ‘normal’ range, but you might still be considered overweight by a doctor even if your BMI technically puts you in the healthy range of BMIs.  On the other hand, if your BMI is higher than you thought it would be because you’ve never thought of yourself as being overweight, or even anywhere near to be overweight, the problem could be linked to your muscles mass.  If you have a very developed muscular structure with little fat on it, your BMI might fall in the overweight range even if you are not overweight.

Taking the body’s proportion of muscle and fat into account is one of the important factors when considering overall health.  This is one factor that the BMI does not consider.  Another important factor is the circumference of your waist.  Having a waist measurement that is very large in comparison to your height is another important factor to take into consideration.  A healthy weight is determined by height, muscle and fat percentages, and the measurement of the waist.

If you’re really concerned about getting an accurate idea about just how healthy your weight is, you should take more than your BMI into consideration.  You’ll want to use the BMI as a starting point, then get evaluated for muscle and fat percentages, take your waist into consideration, and, last but not least, consider the weight that you were in your last year of high school.  All adults experience weight gain as part of the natural aging process, but gaining a disproportionate amount of weight in comparison to your senior year weight is a sign that your weight might be getting out of control.  Some doctors recommend trying to stay within ten pounds of their weight on their 18th birthday, but for a lot of people that is a pipe dream.  However, do try to keep it in mind as a general idea of where your weight should be.

Related posts:

1. What Is the Body Mass Index?
2. The Best Definition Of Obesity Is A Body Mass Index Of Thirty Or More
3. Building Muscle Mass: Things You Need to Know