To tell whether a young adolescent has a healthy weight, it can help to know the average for their age and sex. The averages for 12-year-olds are 89 pounds, for males, and 92 pounds, for females.

However, beyond biological sex, many other factors influence someone’s weight at this age, including their height, body composition, the onset of puberty, environmental factors, and underlying health issues.

Below, we explore the averages and the factors that affect them, using statistics from the Centers for Disease Control and Prevention (CDC).

We also describe some health risks of having a weight that is significantly below or above average.

## The averages by sex

Biological sex plays a role in weight, and in general, a 12-year-old female weighs slightly more than a male of the same age.

When discussing a child’s weight, a doctor may refer to a statistic that indicates the percentage of others who weigh less or more.

For example, a child in the 35th percentile weighs more than 35% of children of the same age and sex. By the same token, they weight less than 65% of these peers.

### Females

According to the CDC, the average weight of a 12-year-old female is 92 pounds (lb), or around 42 kilograms (kg).

Below, find the average range by percentile:

 Percentile lb kg (rounded to nearest value) 95th 135 61 90th 123 56 75th 106 48 50th 92 42 25th 81 37 10th 72 33 5th 68 31

### Males

The CDC report that the average weight of a 12-year-old male is 89 lb, or about 40 kg.

Below, find the average range by percentile:

 Percentile lb kg (rounded to nearest value) 95th 130 59 90th 119 54 75th 103 47 50th 89 40 25th 79 36 10th 71 32 5th 67 30

## Complications of low or high weight

A doctor may be concerned about the weight and health of a young adolescent if:

• their weight falls within the 3rd percentile
• their weight falls beyond the upper or lower percentiles on the CDC’s growth chart
• there has been a drastic change in their weight

When their weight falls significantly above or below the average, a young adolescent may have a risk of health complications. We outline some examples below.

### Complications of low weight

Doctors may use the expression “failure to thrive” when describing a child with poor weight gain or sudden weight loss. The expression usually applies to babies and toddlers, though older children can also have difficulty gaining or maintaining weight.

The following are some potential causes of slow weight gain in children:

• Premature birth: This can lead to the underdevelopment of certain muscles.
• Down syndrome: This chromosomal condition can lead to delayed development of certain muscles.
• Metabolic disorders: These can interfere with the body’s ability to convert food into energy.
• Cystic fibrosis: This inherited condition can prevent the absorption of calories.
• Food allergies or intolerances: These can limit meal options.
• Gastroesophageal reflux: This digestive condition can lead to frequent vomiting.
• Stress: Those relating to home life or school, for example, can affect a child’s appetite.
• Financial difficulties: These can make it difficult for parents and caregivers to provide sufficient food.

A child with very low weight may have:

• developmental delays
• problems with thinking
• behavioral issues
• problems at school
• below-average height

### Complications of high weight

Children and young adolescents with overweight or obesity may have an increased risk of:

As the CDC note, children with obesity are also more likely to develop severe obesity and associated risk factors as adults.

## How weight relates to BMI

A healthcare provider may calculate a child’s body mass index (BMI) to determine whether their weight is healthy. This gives a more accurate picture because it also takes height into account.

The CDC provide a tool for calculating the BMI of children aged 2–18 years. To use it, a person needs to know:

• the child’s weight, in pounds
• the child’s height, in inches
• their child’s age, in months or years and months

The calculator gives the child’s BMI as a percentile and more information.

## Other factors to consider

A range of things can influence the weight of a 12-year-old. Below are several to keep in mind when determining whether a young adolescent has a healthy weight:

### Height

A person who is shorter generally weighs less than someone taller, and this is why BMI calculators take height into account.

Two children who weigh the same but are 6 inches apart in height will have different BMIs. For example, the shorter of the two children may have overweight, while the taller may have a weight in the healthy range.

### Puberty onset

During puberty, adolescents experience growth spurts and other physical changes that increase their weight.

According to Stanford Children’s Health, males typically enter puberty between the ages of 9.5 and 14, and females do so between the ages of 8 and 13. However, these are only estimates — individuals may start puberty earlier or later.

### Genetics

Their genetic makeup may make some people more susceptible to obesity. However, diet and exercise also play important roles in determining a person’s weight.

### Body composition

When assessing weight, it is important to consider a person’s body composition.

A child with a higher-than-average amount of body fat may weigh more than average — and so may a child who is physically active and has significant muscle tone. This is because muscle has a higher density than fat.

### Environment

Environmental factors can significantly influence a child’s weight, and the effects may begin in utero.

Some of these factors include:

• eating many high-calorie, processed foods
• having a sedentary lifestyle
• having high levels of stress
• not getting enough sleep

### Illnesses

Some examples of health conditions that can lead to weight gain in children and adolescents include:

Some examples of those that can lead to weight loss in children and adolescents include:

## Summary

The average weight of a 12-year-old varies by biological sex — for females, it is 92 lb, and for males, it is 89 lb.

However, for a more accurate idea of whether a young adolescent’s weight is healthy, it is important to consider factors such as their height and body composition, and whether they have entered puberty.

When a 12-year-old’s weight falls significantly above or below the average, they may be at risk of developing complications. Anyone with concerns should take their child to a pediatrician.