Length for girls at 4 months

At 4 months, the median length for girls on the WHO Child Growth Standards is 62.1 cm (24.4 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 60.6 and 63.5 cm, a spread of 2.9 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 57.8 and 66.4 cm.

Since 3 months, the median has risen by 2.3 cm in one month. By 5 months it reaches 64.0 cm. That monthly change is smaller than the 4.5 cm of the first month, because growth slows steadily through the first two years.

For boys at 4 months the median is 63.9 cm, 1.8 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 4 months is 61.5 cm. A girl exactly on the WHO median would read as about the 59th percentile there, one reason two charts can give different answers for the same length.

Reading the table: a girl at 4 months who measures 63.0 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.