The Centers for Disease Control and Prevention explains that healthy weight ranges cannot be defined specifically for teens because their weight fluctuates often according to their age, sex and height. The CDC advises that the best way to assess a teen's weight is to calculate the teen's body mass index.
BMI is considered an adequate measurement of body fat. The CDC has a convenient online tool available to calculate a teen's BMI, which factors the teen's weight and height together and plots the resulting ratio onto a growth chart to determine a percentile ranking. The resulting placement of the teen's ratio on this chart helps to determine whether or not the teen is considered to be in a healthy weight range.