If you have concerns about your health, chances are you have heard or read about body mass index, or BMI. Up until the 1980's, body mass index wasn't the standard used to determine healthy weights. Before BMI, simple tables were used --one for men and one for women-- to calculate weight per inch of height. But since BMI was introduced and used regularly, starting in the 1980's and gaining in popularity in the 1990's (when the vast problem of obesity came more into the public eye), we've had a more accurate way to test for obesity and healthy weights.

What, exactly, is body mass index? Like its forerunner, the height and weight table, body mass index uses height and weight to measure for obesity. What makes BMI different, though, is that it is standardized and very simple to use and understand. There is only one calculation to make, which is the same for both men and women. As long as you are an adult over twenty years old, BMI is always calculated in the same way.

Whether you are located in the US or England or in a country that uses the metric system, BMI is generally calculated using metric measurements. That is, it's a persona's weight in kilograms divided by their weight (squared) in meters. To calculate an adult BMI using the Imperial (English or American) system, follow the following formula:

- Multiply your weight in pounds by 703.
- Divide that number by your height in inches, squared. (To square your height in inches, simply multiply that number by itself. So if you are 5'5, that's 65 inches. Your height squared (65 x 65) is 4225.)
- Round the first decimal point up if needed, and you have your BMI.

Or, even easier, simply use one of the countless BMI calculators available for free on the web.

So you have your BMI number. How do you know if your BMI says you are obese? Do you think you need to start a healthy weight loss? There are a lot of resources on the web that will tell you, but we'll put that information here, too, just in case.

Underweight - BMI of under 18.5
Normal - BMI of 18.5 to 25
Overweight - BMI of 25 to 30
Obese - BMI of 30 to 40
Morbidly Obese - BMI of greater than 40

As you can see, BMI is a simple and generally accepted way to calculate the health level of your current healthy weight. It's important to note, though, that BMI is not foolproof, and there are some factors that may skew or change the results. Women, for instance, will generally have a higher quantity of body fat at the same BMI as a man. And highly trained athletes may have a misleadingly high BMI due to a large amount of muscle mass.