Head circumference for boys at 2 months

At 2 months, the median head circumference for boys on the WHO Child Growth Standards is 39.1 cm (15.4 in): half of boys this age measure less and half more. The middle half of boys, from the 25th to the 75th percentile, falls between 38.3 and 39.9 cm, a spread of 1.6 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 36.8 and 41.5 cm.

Since 1 month, the median has risen by 1.9 cm in one month. By 3 months it reaches 40.5 cm. That monthly change is smaller than the 2.8 cm of the first month, because growth slows steadily through the first two years.

For girls at 2 months the median is 38.3 cm, 0.9 cm less than for boys, which is why the charts are drawn separately by sex.

On the older CDC 2000 infant charts, which some clinics and websites still use before age 2, the median at 2 months is 39.9 cm. A boy exactly on the WHO median would read as about the 31st percentile there, one reason two charts can give different answers for the same head circumference.

Reading the table: a boy at 2 months who measures 39.5 cm is at about the 62nd percentile, meaning that out of 100 boys this age, about 62 measure less.