Length for boys at 1 month

At 1 month, the median length for boys on the WHO Child Growth Standards is 54.7 cm (21.5 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 53.4 and 56.0 cm, a spread of 2.6 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 50.8 and 58.6 cm.

Since birth, the median has risen by 4.8 cm in one month. By 2 months it reaches 58.4 cm.

For girls at 1 month the median is 53.7 cm, 1.0 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 1 month is 54.7 cm. A boy exactly on the WHO median would read as about the 51st percentile there, one reason two charts can give different answers for the same length.

Reading the table: a boy at 1 month who measures 55.5 cm is at about the 65th percentile, meaning that out of 100 boys this age, about 65 measure less. Under 2, this is length measured lying down. If a child under 2 was measured standing, WHO adds 0.7 cm before comparing.