Body Mass Index - Know your BMI

Body Mass Index or BMI simply assesses your weight relative to your height. It's a simple, non-invasive method to estimate body composition.

Knowing your BMI helps you determine if you're within body weight norms. Being underweight, overweight, or obese for your height and weight signifies implications to your health.

The greater the tendency towards obesity, the greater the risks become for developing pathologies that culminate in cardiovascular problems.

BMI is calculated algebraically by dividing your body weight in kilograms by your height in metres, squared, i.e.,

BMI = Weight (kg) / Height (m²)

-- You are "overweight" if you have a BMI of 25 to 29.9.
-- You are "obese" if you have a BMI of 30 or more.

To make the calculations, you will need the following basic conversion factors:

• 1 pound = 0.454 kg or, 1 kg = 2.2 lbs
• 1 inch. = 0.0254 m or, 1 m = 39.37 in.

Let’s try an example. Suppose you are 5 feet 6 inches and currently weigh 190 pounds.

The first thing we will want to do is to convert both those values to the metric system:

--190 lbs x 0.454 kg per lb = 86.3 kg
--66 in. x 0.0254 m per in. = 1.68 m

Next, we simply plug in our weight and height into the Body Mass Index formula:

BMI = Weight / Height squared = 86.3 kg / (1.68 m)² = 86.3 kg / 2.82 m² = 30.6 kg/m²

Thus, at 5 feet 6 inches and 190 lbs, you would be considered "obese" at a body mass index of 30.6.

To fall back into a "healthy" weight, you would need to reduce your BMI to at least 24.9.

Because your height never changes, you can actually get an idea of what your healthy weight should be by solving for the unknown variable (your new weight):

24.9 (BMI) = new weight / 2.82

24.9 x 2.82 = new weight

70.22 = new weight

Hence, you would need to weigh 70.22 kg or 154.5 lbs (i.e., 70.22 kg x 2.2 lb per kg = 154.48 lbs) to have a BMI of 24.9.

This means you would need to lose 35.5 pounds.

If you're allergic to the metric system, here is a variation of the Body Mass Index formula using the English system:

BMI = Weight (lbs) / Height (in²) x 704.5

Substituting your weight and height, we get:

BMI = 190 lbs / (66 in)² x 704.5 = 190 lbs / 4356 in² x 704.5 = 0.0436 x 704.5 = 30.7 lbs/in²

Here is the full classification of the Body Mass Index:

Generally each 5-unit increase implies a curvilinear augmentation for disease risk.

Ideally, you will want to have a BMI between 18.5 and 24.9.

This range is considered your "healthy" or ideal weight (average risk).

If you are overweight, your risk of disease is considered "elevated" and if you are obese, your risk of disease is "high" (class I), "very high" (class II), and "extremely high" (class III).

You should understand that excess weight is not the only risk to your health.

Being underweight can also place you at risk for gastrointestinal diseases, immune impairment, and certain diseases of the heart related to electrolyte imbalances. If you are underweight, your risk of disease is considered "elevated." You are underweight if your body mass index is less than 18.5.

So it’s important to stay within your healthy, ideal weight range.

Body mass index uses your total body weight and therefore, is often criticized for failing to differentiate between body fat, muscle mass, and bone.

Consider once more, our 5 feet 6 inch individual weighing 190 lbs.

What if I now told you he was a bodybuilder with excellent muscular definition at a body fat percentage of 5 percent.

Would you consider him obese?

Hardly. Yet his BMI at 30.6 would indicate he was a class I obese individual.

So while body mass index is generally thought to accurately reflect body composition in the general population, it may fall a little short with the athletic population.

A very recent 2007 study published in Medicine and Science in Sports and Exercise, the official journal of the American College of Sports Medicine (ACSM)-- recommended new BMI cut-off values for young athletic adults based on their findings.

The researchers recommended a BMI of 27.9 as "overweight" for male athletes, and 27.7 for women athletes. These values are thought to more accurately reflect a body fat percentage of 20 percent and 33 percent for males and females respectively.

Interestingly, the researchers also made recommendations for young non-athletes to better reflect these same body fat percentages. They suggested a body mass index of 26.5 for males and 24 for females.

Such are some of the limitations of body mass index guidelines. The BMI index has its flaws but one of the arguements in favour stems from its wide usage especially in clinical settings-- giving more validity to the results you get.

So take a moment now to calculate your BMI. It’s easy!

And if the formulas above deter you in anyway, try this handy BMI calculator. It does all the calculations for you. And because it's a straight mathematical calculation, this calculator is reliable.

-- BMI Calculator (Body Mass Index)


Let's move on to our next method for assessing your ideal weight-- the waist to hip ratio.

Equally as simple and non-invasive, this one is slightly more telling in that the ratio represents the distribution of body fat....


Go directly to your next topic: Waist to Hip Ratio

Jump from Body Mass Index back to Ideal Weight Section