The standard body mass index (BMI) is a measure of body fat based on height and weight that applies to most adults 20 years and older. It is commonly used to determine if a person is underweight, normal weight, overweight, or obese.
BMI is calculated by dividing weight in kilograms by the square of height in meters. For example, a person who weighs 150 pounds and is 5 feet 9 inches tall would have a BMI of 24.9. This would be considered a normal weight.