Length for girls at 15 months

At 15 months, the median length for girls on the WHO Child Growth Standards is 77.5 cm (30.5 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 75.7 and 79.4 cm, a spread of 3.7 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 72.0 and 83.0 cm.

Since 14 months, the median has risen by 1.1 cm in one month. By 16 months it reaches 78.6 cm. That monthly change is less than half the 4.5 cm of the first month, because growth slows steadily through the first two years.

For boys at 15 months the median is 79.1 cm, 1.6 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 15 months is 77.2 cm. A girl exactly on the WHO median would read as about the 54th percentile there, one reason two charts can give different answers for the same length.

Reading the table: a girl at 15 months who measures 78.5 cm is at about the 64th percentile, meaning that out of 100 girls this age, about 64 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.