Your body-mass index (''BMI'') measures your height/weight ratio. It is your weight in kilograms divided by the square of your height in meters.
For instant, if your height is 1.82 meters, the divisor of the calculation will be (182 * 182) = 3.3124. If you weigh 70.5 kilograms, then your BMI is 21.3 (70.5 / 3.3124). People with BMIs between 19 and 22 live longest.
Death rates are noticeably higher for people with indexes 25 and above. (5/1/2001: The U.S. government recently changed these ranges to a minimum of 20 and a maximum of 24. I encourage you to take these numbers with a grain of salt; they are not as accurate as they sound.)