Baby Head Circumference Percentile
The Baby Head Circumference Percentile Calculator shows where your baby's head size falls compared with other children of the same age and sex. Enter your baby's age, sex, and head circumference, and it estimates the percentile against WHO growth references. A percentile of 50 means an average head size; very low or very high values are worth discussing with your pediatrician.
Rates and fees change frequently. Always confirm the current figures
with the official authority before relying on this result.
- Approximate estimate using WHO medians. Clinicians use full LMS charts for precise percentiles.
Formula
z = (head circumference − median) ÷ SD; percentile from the normal distribution (WHO reference).
- The percentile compares your baby's head circumference to the distribution of sizes for their age and sex.
- A z-score is computed as z = (head circumference − median) ÷ SD, then converted to a percentile using the normal distribution.
- Medians come from WHO head-circumference-for-age references and are interpolated between the charted ages.
- Input definitions: • Gender: boy or girl, since growth references differ by sex. • Age: the baby's age in months (0–60). • Head circumference: the measured distance around the head, in centimetres.
- This is a screening estimate using approximate standard deviations — clinicians use full LMS charts for precise percentiles.
- Head growth that suddenly crosses percentile lines, in either direction, should be reviewed by a doctor.
Example Calculation
Inputs
- Gender: boy
- Age: 6 months
- Head circumference: 43.3 cm
A 6-month-old boy with a 43.3 cm head circumference sits right at the WHO median for his age, so the estimated percentile is about the 50th — a typical head size.
Frequently asked questions
What does a head circumference percentile mean?
It tells you how your baby's head size compares with other babies of the same age and sex. The 50th percentile is average; the 90th means larger than 90% of peers.
What percentile is normal?
Anywhere between roughly the 3rd and 97th percentile is generally considered typical. Consistency over time matters more than a single number.
Why measure head circumference?
It's a key marker of brain growth in infancy. Unusual size or a rapid change in percentile can prompt a doctor to look more closely.
How do I measure my baby's head?
Wrap a soft tape around the widest part — above the eyebrows and ears and around the back of the head — and read the measurement in centimetres.
Should I worry about a low or high percentile?
Not on its own. Many healthy babies sit at the extremes. Your pediatrician interprets it alongside other growth measures and your baby's history.
How accurate is this estimate?
It uses WHO medians with approximate standard deviations, so it's a screening estimate. Clinicians use detailed LMS charts for exact percentiles.
Related calculators
Baby Weight Percentile Calculator The Baby Weight Percentile Calculator shows where your baby's weight ranks against other children of the same age and sex. Enter the age, sex, and weight, and it estimates the percentile using WHO weight-for-age references, plus the median weight for that age. A percentile of 50 is average; very low or very high values are worth discussing with your pediatrician. Baby Height/Length Percentile Calculator The Baby Height/Length Percentile Calculator shows where your baby's length or height ranks against other children of the same age and sex. Enter the age, sex, and measured length, and it estimates the percentile using WHO growth references, along with the median height for that age. The 50th percentile is average; very low or very high values are worth raising with your pediatrician. Baby Age Calculator (Weeks & Months) The Baby Age Calculator tells you exactly how old your baby is in weeks and in months. Enter your baby's date of birth and today's date, and it returns the age in weeks (plus extra days), the number of completed calendar months, and the total days lived. It's handy for tracking milestones, vaccination schedules, and age-based clothing or feeding guides.