Calculating Your Child’s BMI

Nearly 1 in 3 kids are overweight or obese. Paying attention and calculating your Child’s BMI will help you and your child get away from this scenario. Having an undesired weight pose significant health risks during childhood. It also has the potential of becoming more serious towards adulthood.
At a Glance
  • The Body Mass Index (BMI) is an inexpensive technique of screening and identifying early signs of weight issues that may lead to a series of health problems. One’s BMI is determined by his height and weight.
  • BMI calculation is different for adults and children. Age- and gender-specific charts are used to evaluate people’s BMI, and it is very important to use only the proper BMI calculator or chart in assessing the BMI of a particular person.
  • To calculate your child’s BMI, divide his weight by his heigh squared and multiply the result to the factor 703 [BMI = weight/(height x height) x 703].
  • The BMI percentile is a tool to categorize a child’s BMI based on the child’s gender and age group. Classic weight categories include:
    – Underweight
    – Normal
    – Overweight
    – Obese
  • Alternative measure to BMI are available. The Body Adiposity Index (BAI) multiplies hip circumference by height. An old alternative is measuring waist circumferences (men with a waist circumference above 40 inches and women above 35 inches are at risk of getting heart disease and other medical conditions). Another is calculating waist-to-hip ratio (normal ratio is above 0.90 for men and above 0.80 for women. Body fat can also be measured using calipers.

BMI Calculator

What does BMI stand for?

Many believe that Body Mass Index (BMI) indicates “body fatness.” To set it straight, it is not necessarily a measurement of fat. Some studies show its direct correlation to one’s BMI measurement- determined using weight and height measurements. BMI is an inexpensive technique of screening and identifying early signs of weight issues that may lead to a series of health problems.

Age- and gender-specific charts are used to evaluate the BMI of children and teens. Take note that body fat differs for boys and girls as they mature and undergo physical changes.

Closeup image of baby's feet standing on digital weight scales measuring body mass index

Why is BMI important?

BMI doesn’t measure the body fat of your child. It is used to categorize children if they are underweight, normal, overweight, or obese. The BMI measurement of older children has a strong correlation to the amount of body fat, which may suggest risks of acquiring weight-related disorders in the future.

Identifying who is at risk is essential to your child, to you as a parent, and to your healthcare provider. Your child’s doctor can monitor his weight and recommend healthy calorie intake and exercise habits to prevent adult obesity.

BMI chart by age and height

By Height & Weight

BMI Table Girls 5–18 Years (WHO 2007)

5:012.7-16.917.0–18.9 19.0 or higher
5:612.7-16.917.0–19.0 19.1 or higher
6:012.7–17.0 17.1–19.2 19.3 or higher
6:612.7–17.117.2–19.5 19.6 or higher
7:012.7–17.317.4–19.8 19.9 or higher
7:612.8–17.5 17.6–20.1 20.2 or higher
8:012.9–17.7 17.8–20.620.7 or higher
8:613.0–18.0 18.1–21.021.1 or higher
9:013.1–18.3 18.4–21.5 21.6 or higher
9:613.3–18.7 18.8–22.022.1 or higher
10:013.5–19.019.1–22.622.7 or higher
10:613.7–19.4 19.5–23.1 23.2 or higher
11:013.9–19.9 20.0–23.723.8 or higher
11:614.1–20.3 20.4–24.324.4 or higher
12:014.4–20.820.9–25.025.1 or higher
12:614.7–21.3 21.4–25.625.7 or higher
13:014.9–21.8 21.9–26.2 26.3 or higher
13:615.2–22.3 22.4–26.826.9 or higher
14:015.4–22.7 22.8–27.3 27.4 or higher
14:615.7–23.1 23.2–27.827.9 or higher
15:015.9–23.5 23.6–28.2 28.3 or higher
15:616.0–23.823.9–28.6 28.7 or higher
16:016.2–24.1 24.2–28.929.0 or higher
16:616.3–24.3 24.4–29.1 29.2 or higher
17:016.4–24.5 24.6–29.3 29.4 or higher
17:616.4–24.624.7–29.4 29.5 or higher
18:016.4–24.824.9–29.5 29.6 or higher

BMI Table Boys 5–18 Years (WHO 2007)

5:113.0–16.6 16.7–18.3 18.4 or higher
5:613.0–16.716.8–18.4 18.5 or higher
6:013.0–16.8 16.9–18.5 18.6 or higher
6:613.1–16.917.0–18.7 18.8 or higher
7:013.1–17.0 17.1–19.0 19.1 or higher
7:613.2–17.217.3–19.3 19.4 or higher
8:013.3–17.4 17.5–19.7 19.8 or higher
8:613.4–17.7 17.8–20.120.2 or higher
9:013.5–17.9 18.0–20.5 20.6 or higher
9:613.6–18.218.3–20.9 21.0 or higher
10:013.7–18.5 18.6–21.4 21.5 or higher
10:613.9–18.8 18.9–21.922.0 or higher
11:014.1–19.219.3–22.5 22.6 or higher
11:614.2–19.519.6–23.023.1 or higher
12:014.5–19.920.0–23.6 23.7 or higher
12:614.7–20.4 20.5–24.224.3 or higher
13:014.9–20.8 20.9–24.8 24.9 or higher
13:615.2–21.3 21.4–25.3 25.4 or higher
14:015.5–21.821.9–25.926.0 or higher
14:615.7–22.2 22.3–26.5 26.6 or higher
15:016.0–22.77 22.8–27.027.1 or higher
15:616.3–23.1 23.2–27.427.5 or higher
16:016.5–23.5 23.6–27.928.0 or higher
16:616.7–23.924.0–28.328.4 or higher
17:016.9–24.3 24.4–28.628.7 or higher
17:617.1–24.624.7–29.0 29.1 or higher
18:017.3–24.9 25.0–29.229.3 or higher

How to Calculate Your Child’s BMI

To calculate your child’s BMI, first, you should get the accurate measurements of your child’s height and weight. To do this:

  • Remove your child’s outer layer of clothing, shoes, and any hair accessories.
  • To obtain your child’s height, let your child stand with his or her feet together on a flat surface (uncarpeted floor) with the head, shoulders, back, buttock, and heels placed against the wall.
  • To obtain your child’s weight, use a digital scale placed on a flat surface and let your child stand up on both feet on the center of the scale without extra movements.

BMI Formula for Children

A child’s BMI is calculated by using a standard formula:

weight/ (height x height) x 703

To do this:

  • Measure your child’s weight (lbs)
  • Measure your child’s height (in)
  • Calculate your child’s BMI by dividing the weight by the height squared and multiplying the result to the factor 703 as shown in the formula [Source: CDC].

BMI Percentiles for Children

The BMI percentile is a tool to categorize a child’s BMI based on the child’s gender and age group. Determine the correct BMI percentile by doing the procedure below.

  • Look for the age and sex, which is appropriate for your child on a BMI Chart.
  • Plot your child’s BMI measurement on the BMI chart.
  • Once you are able to determine your child’s percentile, you will then classify your child’s weight against the corresponding range or weight category.

Weight Categories

1. Underweight– having a BMI less than the 5th percentile

2. Normal– having a BMI less than the 85th percentile but not below the 5th percentile

3. Overweight– having a BMI above the 85th percentile but not more than the 95th percentile

4. Obese– having a BMI higher or equal to the 95th percentile

Is BMI 100% reliable?

It is typical for children to grow quickly at the stage of puberty [See: Article on growth charts]. BMI may not be 100% reliable and the doctor can figure out if your child’s weight gain is normal or an indication of a more serious condition. A large frame or greater muscle mass may result in a higher BMI reading. Children with a smaller frame with high body fat may have a normal BMI reading.

It is important for doctors to look at BMI values as a pattern or trend and not an individual number that stands alone.

What if my child’s BMI is too high/too low?

The American Academy of Pediatrics (AAP) together with the Centers for Disease Control and Prevention (CDC) recommend the use of BMI to identify children who are overweight or obese from ages 2 to 19 years. BMI is not a diagnostic tool to determine whether your child has excess fat. The assessment of a medical professional would be needed.

What are pros and cons of BMI?

For the simple reason that BMI is used to categorize children based on their weight, it helps in the prevention of your child’s risks of developing or acquiring abnormal health conditions. High BMI values of older children are highly correlated to body fat.

It can be used as an indicator of these health consequences:

Health Risks Today

  • High blood pressure and high cholesterol are common risk factors for the development of cardiovascular disease (CVD). Studies show 70% of children categorized as obese suffer from one risk factor.
  • Higher risk of insulin resistance, impaired glucose metabolism, and type 2 diabetes.
  • Development of breathing disorder like apnea and asthma.
  • Problems with bones and joints.
  • Heartburn, GERD, the formation of gallstones, and fatty liver disease
  • Behavioral problems, depression, and psychological stress
  • Low self-esteem.
  • Impairment of physical, social, and emotional aspect.

Health Risks in the Future

  • Children who are classified as obese have a high chance of turning to an obese adult. Adult obesity is associated with some serious health conditions like heart ailments, diabetes, and other forms of cancer.
  • Overweight children can become obese adults.

In the recent years, the use of BMI had been questioned and plagued with controversies. BMI accurately calculates the proportion of your child’s weight versus your child’s height. BMI fails to cover the criteria below:

  • It doesn’t differentiate body fat from muscle mass. Assuming that an athletic child develops a high percentage of muscle mass, he or she may fall into the overweight category.
  • The bone density of a child is not taken into account.
  • The BMI values don’t represent a healthy weight. Weight should depend on the starting weight of a child, genetics, gender, and other factors.

Are there alternative measures to BMI?

Existing controversies and issues with the use of BMI lead to the development of alternatives or methods. Combining these methods can give you more accurate data.

Body Adiposity Index (BAI)

There are few conducted clinical trials to support the claim that BAI values are more accurate. The Body Adiposity Index is useful in areas where there is no scale like mountainous areas or deserts. To compute for BAI, multiply the hip circumference by the height.

Waist Circumference Measurement

One of the old alternatives to BMI is the use of a measuring tape. By measuring the circumference of your waist, it may be a good indication of the amount your body fat. According to physicians, men with a waist circumference above 40 inches, and women with a waist circumference above 35 inches are at risk of getting heart disease and other serious medical conditions.


This method requires you to measure your natural waist and the fullest part of your hip with a measuring tape. Divide the circumference of your waist by your hip circumference and interpret the values according to the standards:

< 0.90 < 0.80normal
0.90 - 0.990.80 - 0.84 overweight
1.0+ 0.85+ obese

According to the World Health Organization, a normal waist-to-hip ratio is above 0.90 for men and above 0.80 for women. This method is useful in assessing your susceptibility to acquiring health disorders like heart disease, high blood pressure, and diabetes.

Hydrostatic Weighing

This method is not as popular as the other alternatives. The method requires measuring your weight underwater with a weighing scale. It uses a specific formula for the body-fat reading.

Body Fat Measuring

The easiest and simplest way to calculate your body fat is with the use of calipers. The skin and fat on the shoulder blade, biceps, triceps, and waist are measured. The results are added to obtain a single value which is interpreted against a chart where age and sex are taken into account. The corresponding body fat percentage is subject to reading and interpretation.

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