Growth charts are available online at CDC.gov. The site includes links to charts for the World Health Organization growth standards, which are used for infants between 0 and 2 years old, and the Centers for Disease Control and Prevention growth charts for children 2 years and older.
Growth charts use percentiles to measure children's growth and physical development. A percentile tells what rank an individual child has in relation to other children of the same age and sex. For example, an 18-month-old boy who is at the 75th percentile for weight weighs the same or more than 75 percent of boys his age. This means 25 percent of boys his age weigh more than he does, according to the CDC.