A physician uses a variety of factors to determine a child's normal body weight. But the Body Mass Index (BMI) is one of the most common methods of comparing a child's weight and height with those of other children of the same age and gender. A doctor might chart BMI over time to track trends for your child.
Calculation
To determine your child's BMI, divide the square of her height by her weight. BMI charts typically list values in metric units, meaning that the weight is measured in kilograms and the height is calculated in meters.
Conversion
Most people in the United States measure weight in pounds and height in feet or inches, but you can convert these figures to metric units to determine BMI. A BMI that uses pounds and inches can be converted into a metric BMI by multiplying by 703. A BMI that uses pounds and feet can be converted into a metric BMI by multiplying by 4.88. You also can use an online calculator to determine your child's BMI.
Percentile
The BMI percentile score is more useful for assessing a child's weight than the raw BMI score. This is primarily because a child's height is still changing. A child's BMI percentile score can be determined by consulting the appropriate BMI chart for the child's gender.
Chart
A BMI chart is a graph that measures age on the horizontal axis and the BMI score on the vertical axis. The body of the chart contains a series of BMI percentile curves. A child's BMI percentile score is determined by cross referencing his age with his BMI score. You then can compare this point on the chart with the percentile curves to estimate your child's BMI percentile score.
Normal Range
Your child's percentile score indicates the percentage of children of the same age and gender who have a lower or higher BMI. The normal range for a child's BMI percentile score is between 5 percent and 85 percent. A BMI percentile of less than 5 percent indicates that the child might be underweight. A BMI percentile score between 85 percent and 95 percent indicates the child might be overweight, and a ranking of 95 percent indicate the child could be obese.
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