Check your baby's head circumference percentile using WHO growth charts. Enter age, measurement, and sex for results.
Head circumference is one of three key growth measurements pediatricians track during well-child visits. It reflects brain growth and is especially important during the first two years when the brain grows most rapidly.
The WHO head-circumference-for-age charts compare your baby's measurement to healthy children worldwide. A baby at the 40th percentile has a head circumference larger than 40% of babies the same age and sex.
This calculator provides an approximate percentile based on simplified WHO data for boys and girls from birth to 24 months. Unusual head growth patterns (too fast or too slow) may warrant further evaluation, so always share results with your pediatrician. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process. This tool handles all the complex arithmetic so you can focus on interpreting results and making informed decisions based on accurate data.
Head circumference tracking helps detect conditions like microcephaly (small head), macrocephaly (large head), or hydrocephalus (fluid buildup). Early detection is crucial for timely intervention. This tool helps you monitor between pediatric visits. Having a precise figure at your fingertips empowers better planning and more confident decisions. Manual calculations are error-prone and time-consuming; this tool delivers verified results in seconds so you can focus on strategy.
Z-score = (Measured HC − Median HC for Age/Sex) / Standard Deviation Percentile from z-score via normal CDF. Measure at the widest point: above eyebrows and ears, around the occipital prominence.
Result: ~55th percentile
A 6-month-old boy with a head circumference of 17.3 inches (43.9 cm) is near the 55th percentile. The WHO median for boys at 6 months is approximately 43.3 cm, so this baby is slightly above average — perfectly normal.
A newborn's brain is about 25% of adult size. By age 1, it's about 75%, and by age 2, approximately 80%. This rapid growth is why head circumference is such an important marker in early childhood. Any disruption to this growth pattern deserves attention.
Babies are born with soft spots (fontanelles) that allow the skull to expand as the brain grows. The anterior fontanelle typically closes between 12-18 months. If it closes too early (craniosynostosis), the head may not grow properly and surgery may be needed.
Head size is partly genetic. If both parents have larger or smaller heads, their baby likely will too. Familial macrocephaly is common and benign. Your pediatrician will consider family head size when evaluating your baby's percentile.
Head circumference is a proxy for brain growth. Abnormally fast or slow head growth can indicate conditions like hydrocephalus, craniosynostosis, or developmental concerns. It's measured at every well-child visit for the first 2 years.
Any percentile between the 5th and 95th is generally normal. What matters is consistent growth along a curve. A baby who's always been at the 15th percentile is fine; jumping from 15th to 85th warrants investigation.
Microcephaly is defined as a head circumference below the 3rd percentile or more than 2 standard deviations below the mean. It can be caused by genetic conditions, infections during pregnancy, or environmental factors.
Macrocephaly is a head circumference above the 97th percentile. It can be familial (runs in families), benign, or may indicate conditions like hydrocephalus. Your pediatrician will evaluate based on growth trends and family history.
Wrap a flexible tape measure around the widest part of the head: just above the eyebrows and ears, and around the most prominent part of the back of the head (occiput). Pull snug but not tight. Record in inches or centimeters.
Molding from birth or positional plagiocephaly (flat spot) can slightly affect the circumference reading. Measure the actual widest circumference regardless of shape. Report any shape concerns to your pediatrician separately.