Average Head Circumference for a 13-Month-Old Boy

The average (50th-percentile) head circumference for a 13-month-old boy is 46.3 cm (18.2 in), based on the WHO Child Growth Standards. Across the healthy range, most boys this age have a head circumference between 43.9 cm (17.3 in) and 48.8 cm (19.2 in). (measured around the largest part of the head)

What's typical at this age

By the first birthday, head circumference has typically grown about 12 cm since birth. Growth from here is much slower — only around 2–3 cm across the whole second year. Between month 13 and month 14, the median boy's head circumference grows about 0.2 cm.

A percentile compares your boy to other boys the same age — the 50th is simply the middle. Being above or below it is usually completely normal; a baby who has always tracked the 15th or 85th percentile is typically growing exactly as they should. What pediatricians watch for is a sudden change in the pattern, not the number itself.

Percentiles calculated from the WHO Child Growth Standards (2006). For information only — not medical advice. If you're concerned about your child's growth, speak to your pediatrician or health visitor. Full disclaimer.