You can determine if a child is at a normal weight by comparing his body mass index (BMI) to the BMIs of other children with the same age and gender. This technique is commonly used as a preliminary screening tool to identify children who may be underweight or overweight. This procedure requires you to calculate the child's BMI in metric units and consult the appropriate BMI chart to determine the child's BMI percentile score.
Step 1
Weigh your child in pounds with a scale. This example assumes your child weighs 130 lb.
Step 2
Measure your child's height in inches with a tape measure. This example assumes your child is 65 inches tall.
Step 3
Calculate your child's BMI in units of pounds per square inches (lb/in^2.) Divide the weight in pounds by the square of the height in inches. This example shows that the child's BMI is [130 / (65 x 65)] = 0.0308 lb/in^2.
Step 4
Convert your child's BMI from English units of measure to metric units. Multiply the BMI in units of lb/in^2 by 703 to obtain the BMI in units of kilograms per square meter (kg/m^2.) This example shows that a BMI of 0.0308 lb/in^2 is equal to 0.0308 x 703 = 21.6 kg/m^2.
Step 5
Convert the BMI in metric units to a percentile score. Use the appropriate BMI chart for your child's gender to cross-reference your child's age on the horizontal line with your child's BMI on the vertical line. The point of intersection for these two values represents your child's percentile score. Assume for this example that your child is a 14-year old boy with a BMI of 21.6. The point of intersection for these two values shows a BMI percentile of approximately 78.
A BMI percentile between 5 and and 85 percent means that that the child is at a normal weight for his age and gender. A BMI percentile below 5 percent means the child may be underweight, and a BMI percentile above 85 percent means the child may be overweight.
Things You'll Need
- Scale
- Tape measure
- Calculator
- BMI chart
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