A 12-year-old boy who is 4 feet, 11 inches is at a healthy weight between 75 and 104 pounds, according to WebMD's childhood body mass index calculator. A girl with the same age and height has a healthy weight range between 74 and 107 pounds.
Body mass index, or BMI, is a simple calculation to evaluate the presence of body fat, explains the Centers for Disease Control, but it's not a reliable indicator of general health. The BMI calculation for children, known as BMI-for-age, takes age, gender, height and weight into account. WebMD's childhood BMI calculator also provides spaces to input the heights of both parents for a more accurate calculation.