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, or BMI, calculated from a girl's height and weight can be used to determine whether she's 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. By 3 years of age, a child is past the infant and toddler stage. The average weight, shown as 50th percentile on the growth chart, for a 3-year-old 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 44 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 72 pounds. Eleven-year-old girls weigh an average of about 81 pounds and the average for 12-year-old girls is about 92 pounds. As girls grow into teenagers, the range of healthy weights vary widely depending on height.
Average Heights of Girls by Age
Like weight, heights vary by age. The average -- or 50th percentile -- height for a 3-year-old girl is 37 inches, while the average for a 4-year-old is 40 inches, and a 5-year-old is 42 inches. The average for a 6-year-old girl just 45 inches. A 7-year-old girl has an average height of 48 inches, the average for an 8-year-old girl is 50 inches, and a 9-year-old girl is 52 inches. A 10-year-old girl has an average height of 54 inches, the average for an 11-year-old girl is 57 inches and for a 12-year-old girl is 59 inches, and 62 inches is average for 13-year-old girls. Around the age of 14 or 15, height growth slows for many teen girls.
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 molecular biologist Chao-Qiang Lai, in an article published in Scientific American in 2006.
According to HealthyChildren.org. one way to get a rough idea of how tall a girl will be when she's grown is to add the heights of her 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.