Body Mass Index (BMI) is a screening number calculated from height and weight. It's used as a general indicator of whether a person is underweight, normal weight, overweight, or obese. It is not a direct measure of body fat or overall health.
BMI formula
Imperial: BMI = (weight in lbs × 703) / (height in inches)² Metric: BMI = weight in kg / (height in meters)²
Limitations of BMI
BMI can overestimate body fat in athletic people with high muscle mass, and underestimate it in older adults who have lost muscle. It also doesn't capture where fat is distributed — waist circumference is an important additional metric.
Common questions
18.5–24.9 is considered the healthy range for most adults. Your doctor may define healthy differently based on your individual body composition and health history.
For ages 2–19, BMI is expressed as a percentile relative to others of the same age and sex — not fixed categories like adults.
Yes. Athletes and muscular people often fall in the "overweight" BMI range while being metabolically healthy. BMI is one data point — a doctor can assess the full picture.