BMI for Children and Teens

How to calculate BMI for Children and Teens

BMI is a number that is calculated from a child or teen’s weight and height. BMI serves as a fairly reliable indicator of how much of a child or teen’s weight is composed of fat.

BMI does not measure body fat directly. Rather, it is considered an alternative to measuring body fat directly, which is difficult and can be expensive.

How is BMI used with children and teens?

BMI is used as a screening tool to identify possible weight problems. In children and teens, BMI is used to check for obesity, being overweight, being a healthy weight, or being underweight.

How is BMI calculated and interpreted for children and teens?

BMI measures your child’s weight in relation to height. Both height and weight are measured, and the BMI is calculated from those numbers. Next, the BMI is plotted on a chart that compares your child’s BMI to the BMI of other children (growth chart).

To calculate BMI with metric measurements:

  1. Measure weight in kg (kilograms).
  2. Measure height in meters. Then multiply that number by itself to get a measurement called “meters squared.”
    • For example, for a child who is 1.5 m (meters) tall, the “meters squared” measurement would be equal to 1.5 m x 1.5 m, which is equal to 2.25 meters squared.
  3. Divide the number of kg by the meters squared number.

To calculate BMI with English measurements:

  1. Measure weight in lb.
  2. Multiply the number of lb by 703.
  3. Measure height in inches. Then multiply that number by itself to get a measurement called “inches squared.”
    • For example, for a child who is 60 inches tall, the “inches squared” measurement would be equal to 60 inches x 60 inches, which is equal to 3,600 inches squared.
  4. Divide the total from step 2 (number of lb x 703) by the total from step 3 (inches squared).

Charts and calculators are available to figure this out quickly and easily.

Is BMI interpreted the same way for children and teens as it is for adults?

BMI is calculated the same way for children, teens, and adults. However, the criteria that are used to interpret the meaning of BMI differ with age. This is because body fat changes in children and teens as they grow. Also, girls and boys differ in their body fat as they mature. As a result, BMI for children and teens, also called BMI-for-age, is gender specific and age specific. BMI-for-age is plotted on gender-specific growth charts. These charts are used for people from 2–20 years of age.

Health care professionals use the charts to identify underweight and overweight children based on the following guidelines:

  • Underweight
    • BMI-for-age that is below the 5th percentile.
  • Healthy weight
    • BMI-for-age that is at the 5th percentile or higher, but less than the 85th percentile.
  • Overweight
    • BMI-for-age that is at the 85th percentile or higher.
  • Obese
    • BMI-for-age in the overweight range that is at the 95th percentile or higher.

What does it mean if my child is at the 60th percentile?

Being at the 60th percentile means that your child has a higher BMI than 60% of children who are the same gender and age.

Why is BMI-for-age a useful tool?

BMI-for-age is used to identify a possible weight problem that may be related to a medical problem or may increase the risk for medical problems. BMI can also be used to promote changes to reach a healthy weight.

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