The Centers for Disease Control and Prevention (CDC) have set guidelines for healthy weight and body mass index (BMI) in children.
These guidelines can help doctors and parents or caregivers monitor a child’s growth and determine whether they are underweight or overweight, for example.
This article will discuss the average weights for 13-year-old boys and girls, as well as BMI and other factors to consider.
Average weight for girls
There are multiple factors that can affect average weight.
According to the CDC, most 13-year-old girls weigh between 76 and 148 pounds (lb).
The 50th percentile for weight in this group is around 101 lb. This means that about 50% of girls this age weigh less than 101 lb.
If a 13-year-old girl weighs under the fifth percentile, a doctor may classify this as being underweight.
If a 13-year-old girl weighs above the 95th percentile, the doctor may diagnose obesity. However, height comes into play, too.
Here are the percentiles by weight for 13-year-old girls:
| Percentile | Weight |
| 5th percentile | 76 lb |
| 10th percentile | 80 lb |
| 25th percentile | 89 lb |
| 50th percentile | 101 lb |
| 75th percentile | 116 lb |
| 90th percentile | 135 lb |
| 95th percentile | 148 lb |
Average weight for boys
According to the CDC, most 13-year-old boys weigh between 75 and 145 lb.
The 50th percentile for weight in this group is around 100 lb. This means that 50% of 13-year-old boys weigh less than 100 lb.
If a 13-year-old boy weighs under the 5th percentile, a doctor may categorize this as being underweight.
On the other hand, if a boy in this age group weighs more than the 95th percentile, the doctor may diagnose obesity. However, they take height into consideration.
Here are the percentiles by weight for 13-year-old boys:
| Percentile | Weight |
| 5th percentile | 75 lb |
| 10th percentile | 80 lb |
| 25th percentile | 88 lb |
| 50th percentile | 100 lb |
| 75th percentile | 116 lb |
| 90th percentile | 133 lb |
| 95th percentile | 145 lb |
BMI
When calculating a child or teenager’s BMI, it is important to include their age.
BMI is a way to estimate body fat percentage. The calculation incorporates weight and height. A high BMI can indicate high amounts of body fat. It can also indicate an increased risk of weight-related health issues.
For a more accurate assessment of body fat, a person can look into skinfold measurements, underwater weighing, and bioelectrical impedance. However, these tests may be complicated and expensive, and the results tend to correlate well with BMI.
Calculation of BMI is different for adults and children. In children and teenagers, BMI takes age into account, and doctors refer to it “BMI for age.”
The CDC provide a BMI calculator for children and teens. A person enters the child’s height, weight, and sex. The results give the BMI and indicate whether the weight is in a healthy range.
BMI, like average weight, falls into percentiles. These can help parents, caregivers, and pediatricians determine whether a child weighs a healthy amount for their age and height.
| Percentile | Assessment |
| Under the 5th percentile | Underweight |
| 5th to 85th percentile | Healthy weight |
| 85th to 95th percentile | Overweight |
| 95th percentile or over | Obese |
Factors to consider
A range of factors can affect the weight of a 13-year-old, including:
Puberty and development
Puberty is a time of physical change in children and teenagers. It involves the body preparing for sexual maturity.
Puberty typically occurs in girls between the ages of 10 and 14 and in boys between the ages of 12 and 16. The process can be very different for boys and girls.
Puberty can cause height and weight in 13-year-olds to range broadly.
Genetics
Genetics, as well as lifestyle characteristics, such as diet and physical activity, play a role in a child’s weight and body type.
Research suggests that some genes are strongly associated with obesity.
Body composition
The many variables in a person’s body composition can influence how much they weigh. For example, some people are more muscular, and they may weigh more because muscle weighs more than fat. This might particularly affect athletic children.
Also, taller children are likely to weigh more than shorter children, although this is not always the case. Because the BMI calculation takes height into account, it can give a better idea of healthy ranges than weight alone.
Geographic location
The country that a child lives in can contribute to their body composition, weight, and development.
These differences are due to factors such as socioeconomic status, access to nutritious foods, and cultural traditions.
When to see a doctor
A parent or caregiver can take a teenager to a doctor if they are concerned about their growth or development.
If a child is underweight, consuming more calories may help them reach a healthier weight. A doctor can give advice about whether this is necessary and the best way to go about it.
If a child’s weight falls into a range of overweight or obesity, a doctor can give advice about reaching a healthier weight. They may recommend decreasing caloric intake and increasing physical activity.
It is particularly helpful and important for families of children with obesity to work toward healthier habits.
Childhood obesity is associated with a higher risk of:
Also, obesity can extend into adulthood. Researchers have found links between obesity in adulthood and chronic health problems, such as heart disease, type 2 diabetes, and certain cancers.
Any parent or caregiver who is concerned about a child’s growth or development should consult a pediatrician.
Summary
Knowing the average weight of a 13-year-old can help parents and caregivers assess whether a child is underweight or overweight.
However, teenagers going through puberty experience many physical changes, and their weight — and sometimes BMI — can change notably over a short period.
A parent or caregiver who has concerns about a child’s weight, growth, or development should consult a pediatrician.