Weight-for-length for boys at 81 cm

At a length of 81 cm, the median weight for boys on the WHO Child Growth Standards is 10.6 kg (23 lb 7 oz): half of boys of this length weigh less and half more. The middle half of boys, from the 25th to the 75th percentile, falls between 10.1 and 11.3 kg, a spread of 1.19 kg. The outer lines of the chart, the 2nd and 98th percentiles, sit at 9.05 and 12.6 kg.

At 79 cm the median weight is 10.3 kg, so 2 cm of extra length goes with about 0.37 kg more weight at the median. At 83 cm it is 11.0 kg. 81 cm is close to the median length of boys at 17 months (81.2 cm). Weight-for-length compares a child's weight with other children of the same length, whatever their age, which is why it can read differently from weight-for-age for a long or a short baby.

For girls at a length of 81 cm the median is 10.3 kg, 0.34 kg less than for boys, which is why the charts are drawn separately by sex.

On the older CDC 2000 weight-for-length charts, which some clinics and websites still use before age 2, the median at a length of 81 cm is 11.0 kg. A boy exactly on the WHO median would read as about the 33rd percentile there, one reason two charts can give different answers for the same weight.

Reading the table: a boy at a length of 81 cm who weighs 11.0 kg is at about the 66th percentile, meaning that out of 100 boys of that length, about 66 weigh less.