Obesity among children is on the rise, and with increased weight comes risk for diseases like diabetes and heart disease, even for kids. A BMI chart shows a measurement called body mass index. This does not measure exact body fat percentage. BMI charts help children, parents and medical professionals quickly see whether a child is normal, underweight, overweight or obese for his age, weight and height. Percentiles compare the weight limits of children of the same age and provide benchmarks for determining what is healthy.
Calculating BMI
To use BMI charts, you must first calculate BMI. Although BMI does not directly tell you an exact body-fat percentage that you get from using skinfold calipers, underwater weighing or electrical impedance methods, BMI does correspond to body-fat percentage, according to the Centers for Disease Control and Prevention. You can then compare your child's BMI on a BMI-for-age chart to discover your child's BMI percentile. To calculate BMI, use a BMI calculator. Select your child's gender first. Then, enter in the birth date, height measurements in feet and inches, weight measurement in pounds and the date of measurements. Then press the "calculate" button. A BMI calculator such as the one at KidsHealth automatically graphs the BMI results on a percentile chart for you. Otherwise, plot the BMI results yourself by lining up the BMI from the column on the sides with the age in years represented along the bottom of the graph. Lines on the graph mark the 5th, 85th and 95th percentiles so you can see where the BMI fits.
Percentiles
A child has a healthy BMI if his percentile is between the large range of the 5th to 85th percentiles, according to the CDC. Children with lower BMIs, less than the 5th percentile, are considered underweight. Overweight children fall are above the 85th percentile. Any child who has a BMI equal to or greater than the 95th percentile is obese.
Gender and Age
Doctors start measuring BMI with children as young as 2 years of age. Doctors use different charts for male and female children. This is because boys and girls grow at different rates and their body-fat amounts differ as they mature, according to KidsHealth. If calculating the BMI yourself, be sure that you select the correct gender so the online calculator shows you the appropriate chart.
BMI Versus Weight
BMI-for-age charts compare body mass index, not simply weight for age. Although it might be easier to simply compare your child's weight to a weight range for their age, this would not give you as accurate information because a healthy weight changes not only as height increases, but also monthly as a child ages, according to the CDC. BMI takes height into account and the calculations take the year and month of a child's birthday into account, giving a more accurate representation of a child's weight range as healthy, underweight or overweight.
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