Percentile curves
Age in months along the bottom. Lines show the 2nd, 10th, 50th, 90th and 98th percentiles.
Percentiles by month
| Month | 2nd | 5th | 10th | 25th | 50th | 75th | 90th | 95th | 98th |
|---|---|---|---|---|---|---|---|---|---|
| 0 | 31.9 | 32.4 | 32.8 | 33.6 | 34.5 | 35.3 | 36.1 | 36.6 | 37.0 |
| 1 | 34.9 | 35.4 | 35.8 | 36.5 | 37.3 | 38.1 | 38.8 | 39.2 | 39.6 |
| 2 | 36.8 | 37.2 | 37.6 | 38.3 | 39.1 | 39.9 | 40.6 | 41.1 | 41.5 |
| 3 | 38.2 | 38.6 | 39.0 | 39.7 | 40.5 | 41.3 | 42.0 | 42.5 | 42.9 |
| 4 | 39.2 | 39.7 | 40.1 | 40.8 | 41.6 | 42.4 | 43.2 | 43.6 | 44.0 |
| 5 | 40.1 | 40.6 | 41.0 | 41.7 | 42.6 | 43.4 | 44.1 | 44.5 | 45.0 |
| 6 | 40.9 | 41.3 | 41.8 | 42.5 | 43.3 | 44.2 | 44.9 | 45.3 | 45.8 |
| 7 | 41.5 | 42.0 | 42.4 | 43.2 | 44.0 | 44.8 | 45.6 | 46.0 | 46.5 |
| 8 | 42.0 | 42.5 | 42.9 | 43.7 | 44.5 | 45.4 | 46.1 | 46.6 | 47.0 |
| 9 | 42.5 | 42.9 | 43.4 | 44.2 | 45.0 | 45.9 | 46.6 | 47.1 | 47.5 |
| 10 | 42.9 | 43.3 | 43.8 | 44.6 | 45.4 | 46.3 | 47.0 | 47.5 | 47.9 |
| 11 | 43.2 | 43.7 | 44.1 | 44.9 | 45.8 | 46.6 | 47.4 | 47.9 | 48.3 |
| 12 | 43.5 | 44.0 | 44.4 | 45.2 | 46.1 | 46.9 | 47.7 | 48.2 | 48.6 |
| 13 | 43.8 | 44.2 | 44.7 | 45.5 | 46.3 | 47.2 | 48.0 | 48.5 | 48.9 |
| 14 | 44.0 | 44.5 | 44.9 | 45.7 | 46.6 | 47.5 | 48.3 | 48.7 | 49.2 |
| 15 | 44.2 | 44.7 | 45.1 | 45.9 | 46.8 | 47.7 | 48.5 | 49.0 | 49.4 |
| 16 | 44.4 | 44.9 | 45.3 | 46.1 | 47.0 | 47.9 | 48.7 | 49.2 | 49.6 |
| 17 | 44.6 | 45.0 | 45.5 | 46.3 | 47.2 | 48.1 | 48.9 | 49.4 | 49.8 |
| 18 | 44.7 | 45.2 | 45.7 | 46.5 | 47.4 | 48.3 | 49.1 | 49.6 | 50.0 |
| 19 | 44.9 | 45.3 | 45.8 | 46.6 | 47.5 | 48.4 | 49.2 | 49.7 | 50.2 |
| 20 | 45.0 | 45.5 | 46.0 | 46.8 | 47.7 | 48.6 | 49.4 | 49.9 | 50.4 |
| 21 | 45.2 | 45.6 | 46.1 | 46.9 | 47.8 | 48.8 | 49.6 | 50.1 | 50.5 |
| 22 | 45.3 | 45.8 | 46.3 | 47.1 | 48.0 | 48.9 | 49.7 | 50.2 | 50.7 |
| 23 | 45.4 | 45.9 | 46.4 | 47.2 | 48.1 | 49.0 | 49.9 | 50.4 | 50.8 |
| 24 | 45.5 | 46.0 | 46.5 | 47.3 | 48.3 | 49.2 | 50.0 | 50.5 | 51.0 |
All values in cm. The 50th percentile at 12 months is 46.1 cm (18.1 in).
How to read it
Find your baby's age in months, then see which columns their measurement falls between. A baby between the 25th and 50th columns is above 25% and below 50% of healthy babies of the same age and sex in the WHO standards. The CDC uses the 2nd and 98th percentiles (2.3rd and 97.7th) as the cutoffs for a closer look. The CDC recommends these WHO standards for children from birth to 2 years in the US.
Frequently asked questions
What is the average head circumference for a baby boy?
WHO growth standards for boys, birth to 24 months: the median head circumference is 34.46 cm (13.6 in) at birth, 46.07 cm (18.1 in) at 12 months and 48.25 cm (19.0 in) at 24 months.
What percentile is normal?
CDC uses the WHO cutoffs of the 2nd and 98th percentiles (2.3rd and 97.7th) to flag growth worth a closer look. Anything between is within the range of the standards; your doctor looks at how your baby's line moves over time.
Sources: CDC, WHO growth standards data files. Checked October 17, 2026. Not medical advice. Our sources.