The average height and weight for girls vary by age. A girl whose measurements vary from the average isn't necessarily unhealthy, however. Body mass index measurements determined using a girl's height and weight can be used to determine whether a particular girl is at a healthy weight for her height. Numerous factors can affect height and weight, causing a girl to have measurements that aren't average.
Average Weights for Girls by Age
No one average weight for girls exists, since this measurement varies based on age. The average weight for a 1-year-old girl is about 22 pounds; for a 2-year-old girl, it's slightly over 28 pounds. By 3 years of age, the average weight for a girl is almost 31 pounds, and a 4-year-old weighs an average of about 35 pounds.
As girls get older, the average weights increase a bit more per year, with 5-year-olds weighing an average of almost 40 pounds, 6-year-olds weighing an average of about 46 pounds, and 7-year-olds weighing an average of almost 51 pounds. The average weight for an 8-year-old girl is about 57 pounds, the average for a 9-year-old girl is about 64 pounds, and the average for a 10-year-old girl is about 70 pounds. Eleven-year-old girls weigh an average of about 79 pounds.
For older girls, the average weights are listed as ranges rather than individual weights because they can vary so much. For example, a 12- to 13-year-old girl weighs an average of between 95 to 105 pounds, a 14- to 15-year-old girl weighs an average of 105 to 115 pounds, and a 16- to 17-year-old girl weighs an average of 115 to 120 pounds. Eighteen- to 20-year-old girls weigh an average of 125 to 130 pounds.
Average Heights of Girls by Age
Like weight, heights vary by age. The average height for a 1-year-old girl is 28 to 29 inches; for a 2-year-old, it's just slightly higher, at 30 inches. The average height for a 3-year-old is 33 inches, the average for a 4-year-old is 37 inches, and a 5-year-old is 40 inches.
Between the ages of 5 and 6 height doesn't increase very much, with the average for a 6-year-old girl just 41 inches. A 7-year-old girl has an average height of 43 inches, the average for an 8-year-old girl is 45 inches, and a 9-year-old girl is 47 inches. A 10-year-old girl has an average height of 51 inches, and the average for an 11-year-old girl is 52 inches.
As with weight, the average heights for older girls are listed in ranges rather than individual numbers. A 12- to 13-year-old girl's average height is between 60 and 63 inches, a 14- to 15-year-old girl's average height is between 63 and 64 inches, and girls from 16 to 20 years old are an average 64 inches tall.
Healthy Weight for Height
What's more important than knowing whether a girl is at an average height for her age is whether her weight is healthy for someone of her height. This is determined using body mass index, which can be calculated by taking a girl's weight in pounds, dividing by her height in inches, dividing by her height in inches again, and then multiplying by 703. These measurements aren't used quite the same with children as with adults, as there is a wider range of what is normal for any given age due to varying rates of development. A BMI between the 5th and 95th percentile is considered healthy, while one that is higher is considered overweight and below the 5th percentile is considered underweight. For example, while a BMI of 14 would be on the low end of the healthy BMI range for girls between the ages of 3 and 10, it would be considered underweight for older or younger girls. A 10-year-old girl should have a BMI of between 14 and 20, while an 18-year-old girl should have a BMI between 18 and 25.
Factors That Affect Height
A girl's height is mainly determined by genetics, with 60 to 80 percent of what determines height based on genetics, and the remaining 20 to 40 percent determined based on nutrition and other environmental factors, according to an article published in Scientific American in 2006. One way to get a rough idea of how tall a girl will be when she's grown is to add the heights of the father and mother in inches, divide by 2, and then subtract 2.5 inches. A low birth weight, being premature or born at a high altitude, being around cigarette smoke, having low levels of certain hormones, and not getting the proper nutrition can all affect height and cause a girl to be shorter than average.
Certain genetic conditions, medications and chronic illnesses can also affect height, including cancer, severe arthritis, celiac disease, Turner syndrome, down syndrome and Noonan syndrome. If you're worried that you or your daughter isn't growing at a normal rate, consult a physician to discuss your concerns.
Addressing Weight Issues
Being overweight can increase the risk for cancer, asthma, diabetes, joint and sleep problems and heart disease. It isn't a good idea to try to lose weight using fad diets or weight loss supplements, starving yourself or vomiting after eating, however. Instead, pay attention to what and how much you're eating, so you can make healthy changes, and increase the amount of time you spend moving and being active. Eat only when you're hungry, and include both protein and fiber in each meal, as they are particularly filling. Limit fast food and other foods high in sugar or fat and concentrate on eating a mix of lean protein, whole grains, fruits and vegetables.
Being underweight can increase your risk for health problems and impair your immune system. Try to increase the number of calories you're getting from nutritious foods, including those with healthy fats, such as olive oil, avocados, fatty fish and nuts. Eat more often, and choose beverages like smoothies, milk and 100-percent fruit juice that provide nutrients as well as calories.
Parents can help their daughters maintain a healthy weight by limiting screen time to 2 hours per day or less, not keeping snack foods that are high in fat or sugar in the house, and providing balanced meals for the whole family containing plenty of fruits, vegetables and whole grains as well as lean sources of protein. Offer water instead of sugary beverages, and watch the portion sizes you serve. Encourage children to incorporate at least 60 minutes of moderate cardio into their daily routine and do the same yourself to lead by example.