Head Circumference Percentile Calculator
Evaluate your baby's head growth (0–24 months) with WHO reference data.
Use corrected age if your baby was born prematurely.
How to Use This Calculator
Measure correctly
Wrap a flexible tape above the eyebrows and ears, covering the widest part of the back of the head (occiput).
Use corrected age
For premature infants, subtract the weeks born early until 24 months to compare with term-born peers.
Track trends
Significant jumps or drops in percentile, especially with developmental changes, should prompt pediatric evaluation.
Formula
1. Interpolate WHO head circumference averages for the selected age and sex.
Although the WHO uses LMS (Lambda-Mu-Sigma) parameters, this simplified approach closely matches percentile outputs for screening.
About Head Circumference Percentiles
Head circumference is a proxy for brain growth in infancy. Pediatricians measure it at every well-baby visit to screen for conditions such as microcephaly, hydrocephalus, or craniosynostosis.
Accurate measurement technique and serial tracking are vital. One off-percentile may be normal, but consistent trends outside the typical range warrant investigation.
Key considerations
- Compare with parental head sizes—macrocephaly can be familial.
- Assess developmental milestones alongside growth data.
- Premature infants often exhibit catch-up head growth over the first year.
Frequently Asked Questions
How often should head circumference be measured?
At every well-baby visit. More frequent checks may be needed if rapid changes occur.
What if percentile drops suddenly?
Discuss with your pediatrician immediately. Decreases can signal slowed brain growth or measurement error.
Is a large head always concerning?
Not necessarily. Familial macrocephaly is common. Rapid increases, however, require evaluation for hydrocephalus or other conditions.
Can positional plagiocephaly affect measurement?
Mild positional flattening rarely changes circumference significantly, but consistent technique helps ensure accuracy.
Should I measure at home?
Home measurements can reassure between visits, but rely on clinical measurements for important decisions.