Body mass index, often abbreviated as BMI, is a method of comparing your height to your weight. It’s a screening method for identifying individuals who may be significantly above or below their recommended weight. Clinicians commonly use the raw BMI score for adults, while the BMI percentile score is the preferred method of evaluating children. This method allows clinicians to compare a child’s BMI to those of other children in the same gender and age group.
Step 1
Measure the height of a child with a tape measure. Let the child’s height be 49 in. in this example.
Step 2
Measure the weight of a child with a bathroom scale. Let the child’s weight be 97 lb. in this example.
Step 3
Calculate the BMI of the child with the formula BMI = [weight / (height x height)]. The child is 49 in. tall and weighs 97 lb. in this example, so the BMI is [97 / (49 x 49)] = 0.0404 lb./sq. in.
Step 4
Multiply the child’s BMI in units of lb./sq. in. by 703 to obtain the child’s BMI in units of kg/sq. m. The child’s BMI is 0.0404 lb./sq. in. in this example, so the child’s BMI is 0.0404 x 703 = 28.4 kg/sq. m. This step is necessary because BMI charts typically use BMI values in metric units.
Step 5
Select the appropriate BMI chart for the child’s gender and locate the intersection of the child’s age on the horizontal axis and BMI on the vertical axis. Compare this location with the BMI percentile curves to obtain the child’s BMI percentile. Let the child be a girl 18 years old for this example. A BMI of 28.4 kg/sq. m. shows this child’s BMI to be in the 93rd percentile, meaning the child has a BMI higher than 93 percent of 18-year old girls.
Things You'll Need
- Tape measure
- Bathroom scale
- Calculator
- BMI chart
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