There isn't any one ideal weight that is suitable for every teenage girl. What is considered a healthy weight range varies based on a number of factors, including the age, height, weight and developmental state of a particular girl. Although weight is one aspect of a girl's health, it is only one factor that determines overall well-being.
Ideal vs. Average Weight for Age
Not everyone at the same age and height should necessarily weigh the same amount, especially in the teenage years. Body type and stage of development make a difference, as girls tend to gain more body fat as they go through puberty and develop larger breasts and hips. However, you can get a general idea of what is healthy for a girl at a given age by checking the weight-for-age chart from the Centers for Disease Control and Prevention that's used by many pediatricians. For example, at 13 years old, the average weight for a girl is about 101 pounds. The average weight for a 15-year-old girl is about 114 pounds, and that of an 18-year-old girl is about 123 pounds. Keep in mind that these are average weights, not necessarily the ideal weights, which are usually expressed in a range rather than a single number. A person's ideal weight range also depends on her height.
Doctors typically use body mass index percentiles to determine whether a teenage girl is within the right weight range. BMI is calculated by taking your weight in kilograms and dividing it by your height in meters squared. Take your weight in pounds and multiply it by 0.45 to turn it into kilograms, and multiply your height in inches by 0.025 to get your height in meters. Multiply your height in meters by itself to get your height in meters squared. The resulting BMI can then be looked up on a chart that gives BMI-for-age percentiles for girls. Anything between the 5th and 85th percentile is considered normal. For a 13-year-old girl, a BMI between 15.4 and 22.6 is within the normal range. For an 18-year-old girl, an acceptable range would be between 17.6 and 25.6.
While BMI can be a useful screening tool, it shouldn't be the only tool used. It is an estimate of body fat, not an actual measurement. Thus, a girl who is very muscular or has a larger frame may not have a lot of body fat even though she has a higher BMI, while a small-framed girl without a lot of muscle could still have a low BMI even though she has a higher body fat percentage than is healthy.
Other Helpful Measurements
To really determine whether a teenage girl has too much body fat, other tests are needed in addition to the BMI calculation. For example, the doctor may use calipers to determine her skin-fold thickness in different places on the body to get another estimate of body fat or do a test such as underwater weighing or bioelectrical impedance that actually measures body fat. Sometimes the doctor may measure the distance around a person's waist as another potential indicator of whether she is at a higher risk for certain diseases, as carrying too much weight around the waist increases the risk for some conditions.
Cultural Considerations for Teenage Girls
Girls as young as 5 to 8 years old are already becoming dissatisfied with their body and wishing they were thinner, especially if they are exposed to magazines focused on appearance and music television, according to a study published in April 2006 in the Journal of Youth and Adolescence. The media portray very thin girls as the ideal, leading teenage girls to try to become thinner than is healthy or to try to lose weight in unhealthy ways, such as fad diets and skipping meals. In fact, according to a study published in Paediatrics & Child Health in 2004, approximately 33 percent of teenage girls who are already at a healthy weight diet to try to become even thinner, and half of all teenage girls have dieted at some point in their lives.