The BMI, or body mass index, is your body weight divided by the square of your height. Health-care workers use the raw BMI score to establish general weight classifications for adults. The raw BMI score is not as useful in children, since their BMI can change rapidly. Instead, health-care workers compare a child’s BMI with those of other children in the same age and gender group to determine the child’s weight classification. This comparison is the BMI percentile score.
Step 1
Measure your child’s height with a tape measure that uses inches. Weigh your child with scales that use pounds.
Step 2
Divide your child’s height in inches by the square of your child’s weight in pounds. For example, if your child is 47 inches tall and weighs 80 pounds, he has a BMI of 80 divided by (47 x 47), with the result of 0.0362.
Step 3
Convert your child’s BMI from English units to metric units by multiplying by the conversion factor of 703. Your child has a BMI of 0.0362 in this example, so his BMI in metric units is 0.0362 times 703, with the result of 25.5.
Step 4
Determine your child’s BMI percentile score. Locate your child’s age in months on a BMI chart published by the Centers for Disease Control and Prevention. Compare your child’s BMI with the BMI values for your child’s age to determine his BMI percentile score. For example, a 15-year-old boy with a BMI of 25.5 is between the 95th and 97th percentile.
Step 5
Interpret your child’s BMI percentile score. A BMI percentile score below 5 percent means that your child may be underweight. A BMI percentile score from 5 percent to 85 percent is in the normal range. A BMI percentile score from 85 to 95 percent is a warning sign of obesity, and a BMI percentile score greater than 95 percent is an indication of obesity.
Things You'll Need
- Tape measure
- Scales
- BMI chart
- Calculator
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