Weight for girls at 18 months

At 18 months, the median weight for girls on the WHO Child Growth Standards is 10.2 kg (22 lb 9 oz): half of girls this age weigh less and half more. The middle half of girls, from the 25th to the 75th percentile, falls between 9.42 and 11.1 kg, a spread of 1.70 kg. The outer lines of the chart, the 2nd and 98th percentiles, sit at 8.06 and 13.2 kg.

Since 17 months, the median has risen by 0.21 kg in one month. By 19 months it reaches 10.4 kg. That monthly change is less than half the 0.96 kg of the first month, because growth slows steadily through the first two years.

For boys at 18 months the median is 10.9 kg, 0.71 kg 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 18 months is 11.0 kg. A girl exactly on the WHO median would read as about the 25th percentile there, one reason two charts can give different answers for the same weight.

Reading the table: a girl at 18 months who weighs 10.8 kg is at about the 67th percentile, meaning that out of 100 girls this age, about 67 weigh less.