Q: What do growth charts mean?
A: The infant growth chart contains information on the weight, length (height), and head circumference of babies throughout the United States at different ages, so your own baby’s measurements can be compared to theirs. There are different charts for boys and girls. Using the chart, your doctor might find that your son is in the 70th percentile for weight, for example, which means that 70 percent of male babies his age weigh less than he does and 30 percent weigh more. These numbers help your doctor keep tabs on your baby’s size. For many parents, growth charts become a source of anxiety — and competition with other parents — especially if their child is in the lower percentiles. “Don’t worry about a low or high percentile,” says pediatrician Romi Webster of Children’s Hospital Boston. “The most important thing is how your baby grows over time. If he’s small but growing at the appropriate rate, there’s usually no cause for concern.”
Seems quite simple but for some reason I tend to forget. Information from Baby Center.

