One common, but somewhat crude, measure for assessing your poundage is the body mass index, or BMI. Oddly enough, the BMI was created by a Belgian mathematician (perhaps concerned about overindulging on the chocolate delicacies of his countrymen). In any case, the BMI became a surprisingly popular and somewhat controversial way to separate the thin from the fat. To calculate your BMI, you divide your height (in meters) by your weight (in kilograms). Or, you can plug more common pound and inch measurements into this version of the formula:
BMI = weight (lb) * 703 / ( (height * height) (in * in) )
This gives you a single number that ranks your weight. For example,
if you’re five feet eight inches tall (that’s 68 inches total) and weigh 180
pounds, your BMI is 27.4. According to the standard BMI groupings, that
puts you into the overweight category.
If you don’t want to pull out your pocket calculator, you can use one of the many BMI calculators online (just search for “BMI”). Or you can find your spot on the handy BMI chart shown, which helps you judge exactly where you fall in your weight class.
The BMI has some known weak spots. For instance, short, muscular types and athletes can end up in the obese zone even though they’re in prime condition. Similarly, elderly folks can coast through with a normal ranking if they have high body fat combined with very little muscle weight.
Despite these weaknesses, the BMI is good for two things:
• Making conclusions about a population. For example, if the BMI suggests that one-third of Americans are dangerously obese (as it does), the odds are that very few of them are muscular athletes in the prime of their lives.
• Giving a rough idea of the weight situation for an ordinary person. If you fall far outside the normal zone, the BMI is giving you a red warning flag. It’s up to you to follow up and see if you really do have the weight problem it suggests. The standard next step is to measure your waist and analyze your blood.
Source of Information : Oreilly - Your Body Missing Manual (08-2009)