How to Calculate Healthy Body Weight for Children

You can calculate the ideal body weight in many ways, but the body mass index (BMI) is one of the most common. This method compares a person's weight to her height and is performed on people of all ages. This number is then compared to reference values in adults; however, in children the BMI is compared to those of other children with the same age. The BMI does not determine a child's ideal weight by itself and should be used in conjunction with many other factors.

Instructions

1

Find the child's weight in kilograms. If you know the weight in pounds, divide that figure by 2.2 to get kilograms. For instance, if the child weighs 87 lb., this equals 39.54 kilograms.

2

Determine the child's height. For example, suppose he is 4 feet tall. Convert this figure to meters by dividing the feet by 3.28. So the child's height in meters would be 1.22 meters.

3

Calculate the BMI by dividing the weight in kilograms by the height in meters squared. So you would calculate 39.54 / (1.22)^2, or 26.57. Metric units (k / m^2) are used on most BMI charts.

4

Compare the BMI calculated in the previous step to that of other children of the same age and gender as a percentile. You can download such charts from the Centers for Disease Control and Prevention's website (see Resources). Note that the BMI percentile is a unitless measure because it is a comparison of quantities with equal units of measure.

5

Locate the BMI percentile for your child on the correct chart. Use the appropriate chart for your child's gender; locate your child's age on the horizontal line and BMI on the vertical line. The intersection of these values will provide your child's BMI percentile. A BMI percentile in the range of 85 to 95 is considered overweight and a percentile greater than 95 is considered obese. If the child in the example were 12 years old, a BMI of 26.57 would place him above the 95th percentile, so he would be considered obese for his age.

6

Look to the BMI numbers between the fifth and 85th percentiles for the child's age. This range is considered healthy.