A centile chart is a size for age chart that is used to decide whether the size of a child falls within the normal (average) range or whether the child is larger or smaller than normal. The size of a healthy child will increase normally with age. Without knowing a child’s age, one cannot decide whether the size is normal or not. Therefore, accurate ages are needed when using a centile chart.
A centile chart is based on the size measurements of thousands of healthy children recorded at different ages. A centile chart is made up of lines called centiles.
The growth of healthy children usually follows the centile lines.
With increasing age, the centiles move further and further apart, as some normal children grow faster and others slower than the average. As a result, the normal range becomes wider. Boys are slightly larger than girls. However, the same charts are often used for both boys and girls when routinely plotting size-for-age.