Head circumference for girls at 1 month
At 1 month, the median head circumference for girls on the WHO Child Growth Standards is 36.5 cm (14.4 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 35.8 and 37.3 cm, a spread of 1.6 cm. The outer lines of the chart, the 2nd and 98th percentiles, sit at 34.2 and 38.9 cm.
Since birth, the median has risen by 2.7 cm in one month. By 2 months it reaches 38.3 cm.
For boys at 1 month the median is 37.3 cm, 0.7 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 1 month is 37.0 cm. A girl exactly on the WHO median would read as about the 38th percentile there, one reason two charts can give different answers for the same head circumference.
Reading the table: a girl at 1 month who measures 37.0 cm is at about the 65th percentile, meaning that out of 100 girls this age, about 65 measure less.
Percentiles at 1 month
Download CSV (all ages)| Percentile | z-score | Metric | Imperial |
|---|---|---|---|
| 2nd | −2.00 | 34.2 cm | 13.5 in |
| 5th | −1.64 | 34.6 cm | 13.6 in |
| 10th | −1.28 | 35.0 cm | 13.8 in |
| 25th | −0.67 | 35.8 cm | 14.1 in |
| 50th (median) | 0.00 | 36.5 cm | 14.4 in |
| 75th | +0.67 | 37.3 cm | 14.7 in |
| 90th | +1.28 | 38.0 cm | 15.0 in |
| 95th | +1.64 | 38.5 cm | 15.1 in |
| 98th | +2.00 | 38.9 cm | 15.3 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).