BMI is an index of a person’s weight in relation to height.  You can determine your BMI by dividng your weight in kilograms by the square of your height in meters.

BMI = weight(kg)/height(m) to 2nd power or weight (lb) x 703 / height (in) to the 2nd power.        
For instance, my BMI would be 167lbs x 703 / 75.5 inches(2) = 20.59

167 x 703 / (75.5 x 75.5) = 20.59       

To convert pounds into kilograms:
lb / 2.2 lb/kg = kg

To convert inches to meters:
in / 39.37 in/m = m                                                                                                                              

According to the “status quo” and mainstream agencies, a healthy BMI ranges from 18.5 to 24.9, yet more than half of all people living in the U.S. are well over 25, considered obese.  This according to the Journal of the American Medical Association.  There are others that are considered to be underweight, which has risk factors as well. 

Now keep in mind that if u r trying to be Mr. Olympia like Arnold S. did when he won at a BMI of 31, this would not be considered overweight.  Also, Blacks are thought to have a greater bone density and protein content than caucasians, so using the BMI standard in its raw form without any adjustments could overestimate the prevalence of obesity with people of Afrikan descent, so please keep this in mind.  Most of us are not vegetarians or vegans, so our weight would be higher.

BMI Ranges
Underweight range (BMI <18.5)

Healthy Weight (BMI 18.5 - 24.9)

Overweight (BMI 25.9 - 29.9)

Obese (BMI 30 - 39.9)

Extreme Obesity (BMI >40)

Source: U.S. Department of Agriculture and U.S. Department of Health and Human Services, Nutrition and Your Health:Dietary Guidelines for Americans (Washington, D.C.: 2000), pg. 7.