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Childhood Obesity Worries: How Much Should an 11-year-old Weigh?

What's a normal weight for 11 to 13-year-olds? Understanding BMI for tweens and what to do if your child is overweight or obese.
Childhood Obesity Worries
Updated: September 8, 2023
Medically reviewed by  Shari Nethersole, M.D.
Table of contents

Is your child overweight or is it just “baby fat?”

Kids are supposed to fill out and gain weight during their adolescent years. But all children are built differently and grow at different rates, so it can sometimes be difficult to figure out whether your child is at a healthy weight for their age.

If your child is heavier than others in their age group, it’s not necessarily a reason to be concerned. Some children may experience a growth spurt and put on pounds earlier in puberty than their peers. 

 Girls tend to grow taller and gain more body fat at a younger age than boys which can make them appear to be overweight. Body image is a very sensitive topic, especially for kids and tweens, so parents should be careful about how they approach the topic of weight, diet, and exercise

Related: Overweight Kids and Discrimination

That being said, if your child is overweight or obese, it’s important to help them make some lifestyle changes and seek out other ways to help them maintain a healthy weight.

Ask an Expert: What Do You Do When Your Child is Overweight? 

Shari Nethersole, a physician at Boston Children's Hospital and an instructor in Pediatrics at Harvard Medical School offers the following advice for parents worried about their child’s weight. 

 What you want to do is focus on healthy eating behaviors. The number of meals isn't important; the type of food in each meal is. 

For children who are considered medically obese, it would probably be helpful to meet with a nutritionist to review your family’s eating habits and get some information about making appropriate food choices. 

Should I Be Worried About My 11-Year-Old Child's Weight? 

According to data collected by the American Academy of Pediatrics (AAP), obesity affects the health of over 14 million children in the U.S. Kids who are obese face increased risks of high blood pressure and related health problems as adults.

An 11-year-old is just approaching puberty and should continue to have their annual well-check exams to make sure they’re staying fit. Their pediatrician will take their height and weight at these checkups and calculate their body mass index (BMI). A pediatrician will also be able to pinpoint your child’s weight percentile using the Centers for Disease Control and Prevention (CDC) growth charts.

Is My Child Overweight or Is It Just a Growth Spurt? 

Kids experience a pretty significant growth spurt at the onset of puberty. Girls generally go through this spurt around age 12, while boys tend to start growing a couple of years later.

Female doctor measuring overweight boy in clinic

You may be amazed at your child’s growth once they hit puberty. Girls and boys grow about 2 to 3 inches taller per year. After getting taller, kids fill out. Both boys and girls will add about 6 to 7 pounds to their body weight each year, but boys will gain more muscle while girls will gain more fat, as breasts and hips develop.

It’s important to reassure your child that it’s normal to gain weight during this time. Girls especially may be at an increased risk of developing an eating disorder. Help your daughter feel comfortable with her body and focus on healthy eating and exercise rather than appearance or the numbers on the scale.

If you are concerned about your child’s weight gain, speak privately to their pediatrician. Their healthcare provider can determine whether they might be overweight using a BMI calculator.

If it does turn out that your child is at an unhealthy weight, be mindful when you speak to them about it. Healthy lifestyle habits should always be at the forefront of the conversation. Think about your words and make sure they are kind and caring—it matters when you’re talking to tweens.

What Is Body Mass Index? 

Body mass index (BMI) is taken using a person’s height and weight. The resulting numbers tells you whether the person is at a healthy weight, underweight, overweight, or obese.

You can calculate BMI by taking the person’s weight in kilograms and dividing it by the square of the person’s height in meters (be sure to convert standard measurements such as pounds, feet, and inches into metric units when calculating BMI).

Let’s take an example. Edwina weighs 54.4 kilograms, and she is 1.6 meters tall. The square of 1.6 is 2.56 (1.6 * 1.6 = 2.56).

To find Edwina’s BMI, we take her weight, 54.4, and divide it by the square of her height, 2.56. 54.4 / 2.56 = 21.25. She’s within the range of a healthy weight for an 11-year-old girl.

How Reliable is BMI? 

It is important to note that BMI is not a perfect measurement and it should not be used alone to make generalizations about a person’s health.

For example, BMI does not differentiate between muscle mass and fat. As muscle weighs more than fat, a person with a high ratio of muscle mass versus fat might not be unhealthy even if their BMI is high. 

On the contrary, someone with a petite build and minimal muscle mass may have a BMI in the normal range when the amount of body fat on their body is not actually in the healthy range.

If your child has recently hit puberty and sprouted up, they may have a lower BMI but actually, they just haven’t started putting weight on yet. If you have noticed a spurt in their height, it may be best to wait instead of trying to force more food into their diet.

Boy Receiving Check up with the Doctor

Kids who start puberty on the early side may finish most of their height growth and have already begun to fill out. If your girl has recently developed breasts and curves or if your boy has beefed up, their BMI might not be reliable for their age. Take a look at the growth charts and average BMI for kids a few years older than them, and discuss with your pediatrician whether their weight gain may be normal.

BMI is one tool among many. It can be a good starting point. If BMI is too high, that’s a sign to take a better look at your child’s overall health.

Healthy BMI for 11-Year-Old Girls and Boys

According to the CDC, the average BMI for an 11-year-old girl is 17.47. However, girls’ BMI may range from 14.08 to 25.91 at this age and still be considered healthy.

The average BMI for an 11-year-old boy is 17.2, but it may range from 14.29 to 24.93.

Calculating Average Weight for 11 to 13-Year-Olds

Genetics and other factors impact weight. The ideal weight for one child will be different than what is considered a normal weight for another. Your child’s height and muscle mass also impact their weight. 

Average Height and Weight for Middle School Boys:

11-year-old boys

Average height: 143 centimeters (4 feet, 7 inches), Average weight:  36 kilograms (79 pounds) 

12-year-old boys       

 Average height: 149 centimeters (4 feet, 10 inches), Average weight: 40.7 kilograms (89 - 90 pounds) 

13-year-old boys 156 centimeters (5 feet, 1 inch), Average weight: 45.8 kilograms (100 - 101 pounds) 

Average Height and Weight for Middle Girls:

11-year-old girls 

 Average height: 144 centimeters (4 feet, 8 inches), Average weight: 37.4 kilograms (82.5 pounds) 

12-year-old girls 

 Average height: 151 centimeters (4 feet, 11 inches), Average weight: 41.8 kilograms (92 pounds)

13-year-old girls 

 Average height: 157 centimeters (5 feet, 2 inches ), Average weight: 46 kilograms (101.4 pounds)

Helping Kids Lose Weight in Healthy Ways

Physical health and fitness are important during childhood. If your child is overweight or obese, it’s important to find healthy ways to help them lose weight.

Start by increasing their physical activities. See if there’s a sport they’d like to join or maybe you and your child can start track running together. Make physical fitness a family value.

Avoid obsessing over the numbers on the scale or thinking too much about calories. Your child shouldn’t need to diet in the sense of reducing portions and counting calories unless their pediatrician sees the need such as if they are obese.

Talk about nutrients and food and help your child choose a variety of healthy, whole foods, including fruits, vegetables, grains, and fats. See where you can cut junk food and discuss it in terms of physical health, not being skinny or fat.

Set goals together and track your progress. Celebrate successes by focusing on their impact on things like strength, mood, and energy.  

Elisa Cinelli

About Elisa

Elisa is a well-known parenting writer who is passionate about providing research-based… Read more

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