12 MONTH REFERENCE · CM
12-month-old baby head circumference percentiles
A first birthday offers a natural point to look back at the record. The trajectory should still be interpreted alongside the baby’s wider health and history.
Head circumference reference at 365 days
Values below are in cm. The columns are reference percentiles, not recommended limits. “12 months” is represented here by 365 days (30.4375 days per month, rounded). Calendar age may differ; use exact dates in the calculator.
| WHO reference | 3rd | 25th | 50th | 75th | 97th |
|---|---|---|---|---|---|
| Girls | 42.34 | 43.98 | 44.89 | 45.81 | 47.45 |
| Boys | 43.65 | 45.20 | 46.06 | 46.93 | 48.48 |
How to use this table
Find the row for the sex used in your baby’s growth record, then compare the measurement in cm. Between two columns means between those reference percentiles. The calculator gives a more precise comparison using daily WHO parameters.
Measure head circumference consistently
Use a non-stretch tape around the widest part of the head, above the eyebrows and ears and around the back. A healthcare professional can confirm the technique and repeat a measurement that seems unexpected.
What this comparison cannot tell you
Head circumference is one part of an assessment. A calculator cannot interpret head shape, development, family history or the reason for a change. The number does not diagnose a condition or establish a growth goal.
Read the head circumference percentile guide or browse other ages and measurements.
Source: WHO Child Growth Standards, expanded daily tables. Values derived with the LMS method and rounded to two decimals. Methodology and limitations.
Review status: Maintained by Baby Growth and technically reviewed on 29 September 2026. Calculations and product ranges are checked against the cited WHO, CDC and manufacturer sources. This independent tool has not received clinical review and does not replace professional care.