The correct proportion of height to weight depends on body size and development. The body composition of each person is different, and in teens, the rate of development is also a factor when figuring the average height-to-weight proportion. The healthy weight range is in relation to height and the amount of bone, muscle and fat in the body.
Teens grow fast as hormones kick in to trigger muscle development and weight gain that cause rapid physical changes. This doesn't always happen at a proportional rate. Teens can grow as much as 10 inches (25 cm.) during these years. Increase in muscle, fat and bone causes rapid weight gain, and what is important when calculating appropriate height and weight is the proportion of the body composition.
A healthy weight range at every age is measured by a scale called the body mass index (BMI). This formula measures the amount of body fat based on a person's height and weight. The BMI chart for teens (under the age of 20) is different than the adult chart because as teens go through puberty the amount of body fat changes and is different for girls and boys. Body mass calculations for teens are specific to age and gender. The BMI chart for teens uses percentiles to determine if the proportion of height to weight is average for an age group and a gender group. The 50th percentile is considered the average in relation to other teens in that age group. The BMI percentiles are indicators of growth rate and where the teen stands in comparison to others of the same age and gender. A teen is considered underweight if he or she is below the 5th percentile, and overweight at above the 85th percentile.
The healthy weight range changes as a teen grows, and that may change each month, and at a different rate for each sex.