The Body-Mass Index (BMI) is the ratio of a person's weight and the square of their height, measured in meters and kilograms. Using United States customary units (inches and pounds), one needs to multiply the BMI ratio by the factor 703.07.
A person with a BMI below 18.5 is underweight, a BMI between 18.5 and 25 is considered normal, and a BMI between 25 and 30 is overweight. Obesity starts at a BMI of 30.
The average adult in the United States is 5' 7" tall and weighs 178 lbs (this represents an average of the statistics for men and women ).