BMI is a way of relating a person's body weight to their height. The body mass index (BMI) is a person's weight in kilograms (kg) divided by their height in meters (m) squared.
The National Institutes of Health (NIH) now defines normal weight, overweight, and obesity according to the BMI rather than by using traditional height/weight charts.
The NIH defines overweight as a BMI of 27.3 percent or more for women and 27.8 percent or more for men. Obesity is reached when a person's BMI is 30 percent or above.