A person's body mass index, a measure comparing height and weight, is one way to assess if he is at a healthy weight. However, in children, BMI should not be the only factor in determining if your child is at a healthy weight. His BMI percentage must also be calculated for a more accurate picture.
Age and Gender
The formula used to calculate BMI in children and teens is for those ages 2 to 19. There are also two different BMI charts, one for boys and one for girls, which you use to determine what BMI percentile your child is in for her age group.
To calculate BMI, measure your child's height and weight, and enter those numbers in the following formula:
BMI = [weight / (height x height)] x 703
After you've calculated your child's BMI, compare this number to your child's age in the correct BMI percentile chart for her gender.
An ideal percentile for your child’s BMI is between the 5th and 85th percentile. A child is considered underweight if he falls below the 5th percentile. Children who fall in the 85th to 95th percentile are at risk of being overweight in the future. A child is considered overweight if he falls above the 95th percentile.
BMI should not be the only tool you use to determine what weight range your child is in. You should consult your child's pediatrician for more ways to calculate her weight and overall health.