How to Calculate Weight Percentile

Weight percentiles are measurements that determine how a child is compared to his peers. Based on statistical analysis of large groups of children, the Centers for Disease Control and Prevention (CDC) develops children growth charts, consisting of weight and height charts and tables. This data is determined and for two age groups and both genders. As an example, consider calculation of the weight percentile for a boy who is 6 years 3 months 10 days old and weighs 52 lbs..

Instructions

• 1

  Calculate age in months using the following formula. Age(months) = 12 x years + months + days/30. Round the result to the nearest 1/2 month (56.2 would be 56.5 months or 61.72 would be 61.5 months). In our example, it would be Age(months) = 12 x 6 years + 3 months + 10 days/30 = 75.333 months = 75.5 months (rounded).

• 2

  Calculate weight in kilograms (kg). Weight (kg) = Weight (lb) x 0.4536. In our example, it would be Weight (kg) = 52 (lb) x 0.4536 = 23.587 (kg).

• 3

  Navigate to the appropriate CDC weight percentile table (see Resources) depending upon gender and the age group.

• 4

  Determine weight percentile at the cross-section of the age and weight in the appropriate CDC table. In our example, using age 75.5 months and weight 23.587 kg from the table "Male age 2 to 20" find that our boy is at 75th weight percentile. It means that 75 percent of his peers (male children of exactly his age) weighs less than him, and just 25 percent are heavier.