The length of baby at birth is far less variable than his weight. On average, a newborn baby measures 50cm (20in). The range goes from 45cm (18in) to 55cm (22in) in a “full term” infant. Males have a slight edge on females.
The increase in length is fairly rapid in the first few months, then it gradually slows down. The increase in the first three months of life, baby will increase in length by about 9cm.
In the second three months, he grows another 8 to 9cm. In the following six months, he increases his length by another 9cm (approximately). The average rate of growth for females is marginally less.
Elaborate charts have been devised by the experts. Most babies grow at the rates indicated on the charts. However, each child is an individual, and will show variations.