How to Calculate BMI for Teens

BMI, or body mass index, measures how much body fat a person has based on his height and weight. Depending on the number, BMI can help doctors and medical professionals identify those who are at risk for health problems resulting from obesity, according to KidsHealth.org. It is important to include gender and age when calculating a teen's BMI because, as the Centers for Disease Control says, "the amount of body fat changes with age and differs between boys and girls." BMI calculators are widely available online.

Things You'll Need

• Age
• Gender
• Height
• Weight
• BMI-for-age growth chart

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Instructions

• 1

  Record the gender and age of your teen.

• 2

  Measure the teen's height in inches and record the results.

• 3

  Measure your teen's weight and record it with the date the weight was taken.

• 4

  Divide the teen's weight by her height squared. Multiply the result by 703. This is the BMI.

• 5

  Plot the BMI number on the CDC's "BMI-for-age" growth charts. See the Resource section for where to obtain a chart. There are different charts for boys and girls. The chart will give you a percentile ranking that will tell you "the relative position of the child's BMI number among children of the same sex and age," according to the CDC. The chart will also place the teen in one of four categories: underweight, healthy weight, overweight or obese.