Head circumference for boys at birth
At birth, the median head circumference for boys on the WHO Child Growth Standards is 34.5 cm (13.6 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 33.6 and 35.3 cm, a spread of 1.7 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 31.9 and 37.0 cm.
By 1 month it reaches 37.3 cm.
For girls at birth the median is 33.9 cm, 0.6 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 birth is 35.8 cm. A boy exactly on the WHO median would read as about the 25th percentile there, one reason two charts can give different answers for the same head circumference.
Reading the table: a boy at birth who measures 35.0 cm is at about the 66th percentile, meaning that out of 100 boys this age, about 66 measure less.
Percentiles at birth
Download CSV (all ages)| Percentile | z-score | Metric | Imperial |
|---|---|---|---|
| 2nd | −2.00 | 31.9 cm | 12.6 in |
| 5th | −1.64 | 32.4 cm | 12.7 in |
| 10th | −1.28 | 32.8 cm | 12.9 in |
| 25th | −0.67 | 33.6 cm | 13.2 in |
| 50th (median) | 0.00 | 34.5 cm | 13.6 in |
| 75th | +0.67 | 35.3 cm | 13.9 in |
| 90th | +1.28 | 36.1 cm | 14.2 in |
| 95th | +1.64 | 36.6 cm | 14.4 in |
| 98th | +2.00 | 37.0 cm | 14.6 in |
WHO charts label z = ±2 as the 2nd and 98th percentiles (exactly 2.3rd and 97.7th), the cutoffs CDC recommends on WHO charts. Values computed with the LMS method from the published tables (retrieved 2026-10-05).