Length for boys at 3 months

At 3 months, the median length for boys on the WHO Child Growth Standards is 61.4 cm (24.2 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 60.1 and 62.8 cm, a spread of 2.8 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 57.3 and 65.5 cm.

Since 2 months, the median has risen by 3.0 cm in one month. By 4 months it reaches 63.9 cm. That monthly change is smaller than the 4.8 cm of the first month, because growth slows steadily through the first two years.

For girls at 3 months the median is 59.8 cm, 1.6 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 3 months is 60.8 cm. A boy 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 boy at 3 months who measures 62.5 cm is at about the 70th percentile, meaning that out of 100 boys this age, about 70 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.