Length for girls at 1 month

At 1 month, the median length for girls on the WHO Child Growth Standards is 53.7 cm (21.1 in): half of girls this age measure less and half more. The middle half of girls, from the 25th to the 75th percentile, falls between 52.4 and 55.0 cm, a spread of 2.6 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 49.8 and 57.6 cm.

Since birth, the median has risen by 4.5 cm in one month. By 2 months it reaches 57.1 cm.

For boys at 1 month the median is 54.7 cm, 1.0 cm more than for girls, 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 53.5 cm. A girl exactly on the WHO median would read as about the 53rd percentile there, one reason two charts can give different answers for the same length.

Reading the table: a girl at 1 month who measures 54.5 cm is at about the 66th percentile, meaning that out of 100 girls this age, about 66 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.