At term, newborn head circumference is about 34 cm around at the median, and most fall roughly 32–36 cm depending on sex and gestational age.
What “Head Circumference” Means
Clinicians measure the occipitofrontal circumference, the largest loop around the skull. The tape crosses the midpoint of the forehead, skims just above the ears, and wraps the most prominent point at the back of the head. The result is your baby’s head size “around.”
How Big Around Is A Newborn’s Head At Birth: Real Numbers
At term, girls and boys cluster close to the mid-thirties in centimeters. The values below come from an international standard built from healthy pregnancies worldwide. The percentiles describe where most babies land.
| Sex | 3rd–97th Percentile (cm) | 50th Percentile (cm) |
|---|---|---|
| Boys | 32.2–36.6 | 34.3 |
| Girls | 31.7–35.9 | 33.8 |
If your newborn arrives a bit earlier or later than 40 weeks, the expected medians shift slightly. A baby at 37 weeks tends to measure smaller than one at 41 weeks.
Why Ranges Matter
Two healthy babies can differ by several centimeters and both be completely normal. Body size, genetics, and gestational age all shape the number. That’s why professionals use percentiles, not a single “ideal.”
Trusted References You Can Check
For ongoing growth from birth to toddler years, the WHO head-circumference standards let you plot where your baby sits today and how that line moves with time. For size recorded right at birth by gestational age, the INTERGROWTH-21st newborn size standards provide week-by-week centiles for boys and girls. These resources are free to use and match the tools pediatric teams rely on. You can download the charts, print a copy, and take it to your next visit so your clinician can mark the dots and talk through what the curve shows.
How To Get An Accurate Measurement
Tools And Setup
Use a flexible, non-stretch tape. Remove hats and bulky hair ties. Keep your baby calm; measure while resting or feeding if that helps.
Step-By-Step
- Seat your baby or hold on your lap. Face forward.
- Place the tape just above the eyebrows, pass it over the tops of both ears, then around the most prominent point on the back of the head.
- Pull the tape snug to compress hair and read to the nearest millimeter.
- Repeat at least twice and record the largest of consistent readings.
Timing
Newborns often have scalp swelling or molding after delivery. Many teams recheck head size once that settles, usually after the first day.
What A “Small” Or “Large” Head Means
A single reading tells only part of the story. Head size is one marker of growth and development and needs context. Clinicians review percentiles, the trend between visits, gestational correction for preterm babies, and the rest of the exam. Words you might hear:
- Microcephaly: head circumference below the 3rd percentile for age and sex.
- Macrocephaly: head circumference above the 97th percentile for age and sex.
Plenty of babies sit near the edges and do well. Some have family patterns with large heads. Others have smaller frames across weight, length, and head size together. Your clinician will connect the dots if anything needs follow-up.
Median Head Size By Term Week
Here’s how the 50th percentile changes from 37 to 42 completed weeks. These figures describe the expected “middle” for healthy pregnancies and show why due date timing matters.
| Gestational Age (weeks) | Boys 50th (cm) | Girls 50th (cm) |
|---|---|---|
| 37 | 33.0 | 32.6 |
| 38 | 33.5 | 33.0 |
| 39 | 33.9 | 33.4 |
| 40 | 34.3 | 33.8 |
| 41 | 34.7 | 34.1 |
| 42 | 35.1 | 34.4 |
How Growth Tracking Works After Birth
Head size rises fast in early months as the brain grows. Teams plot each visit on growth charts and look for a smooth climb that fits the rest of your baby’s pattern. A sudden jump or drop across several percentile lines prompts a closer look and, if needed, more checks.
Term Babies Versus Preterm Babies
Babies born early are plotted by corrected age until about one year. That means their measurements are compared with babies the same number of weeks after the original due date. This avoids false alarms while they catch up.
What Parents Can Watch For
- Rapidly growing head size paired with vomiting, poor feeding, or unusual irritability.
- Head size that isn’t growing over several visits.
- Body weight and length far from head size, such as a large head with low weight.
If any of those patterns show up, your pediatric team may remeasure, review the exam, and choose next steps.
Bigger Heads And Labor
Pelvic shape, baby position, and soft skull bones all matter. The plates overlap during labor, which changes the reading at first. That’s why repeat measurements after swelling subsides give a clearer picture.
Centimeters And Inches
Many charts use centimeters. If your notes are in inches, here’s a quick guide: 32 cm is about 12.6 in, 34 cm about 13.4 in, and 36 cm about 14.2 in. Converting the unit doesn’t change the percentile.
Percentiles And Z-Scores, Made Simple
A percentile tells you what portion of same-age babies measured at or below that number. The 50th is the middle. A Z-score expresses distance from the middle in standard deviations, which helps clinicians compare across ages and measures. Neither label is a diagnosis by itself.
What Atypical Readings Can Trigger
When numbers stay below the 3rd percentile or above the 97th, or when the curve bends sharply, teams may confirm measurements, check family head sizes, and review feeding, sleep, and development. Next steps can include another visit to see the trend, or specific tests if the exam points that way.
What Shapes Head Size At Birth
Parents often ask what sets the number on day one. Genetics plays a clear part. Maternal conditions, nutrition, and placental health contribute too. Babies with larger bodies often have larger heads, and the reverse tends to be true as well. Twins and late-preterm babies often sit a little lower on the scale at first and then climb along their own steady path.
Reading Your Chart With Confidence
Bring questions to each visit. Ask which percentile line your baby follows and whether the dots are steady. Ask how weight and length compare with head size. Ask when the next check will happen and what number would prompt a call. Simple, direct questions help you leave with a clear plan.
Care Tips For Smooth Measurements
- Pick a calm moment; feed first if that settles your baby.
- Hold the tape flat and level across the forehead and occiput.
- Repeat the reading if your baby wiggles or the tape slips.
- Use the same tape each time if you’re tracking at home.
- Pause if needed.
Head Shape And The Tape Path
Newborn skulls vary. Some look long and narrow after a head-down pregnancy. Others look coned right after a long labor. The tape still follows the same landmarks and seeks the largest loop. If the shape is unusual, teams add checks and keep measuring over time.
Why Boys And Girls Differ A Little
Across large datasets, boys run a touch larger at the same gestational week. The gap is small and shows up as a nudge of the percentile lines instead of a sharp split. That is why the tables list centiles separately by sex.
Visits When This Number Gets Checked
Head circumference is part of the newborn exam and stays on the list at each routine visit through the second year. The schedule varies by clinic, yet many families see a steady rhythm: early newborn checks, then monthly or bimonthly visits in the first half-year, and a few more in the next. Each time, the number joins weight and length on the chart so the whole picture stays clear.
When The First Reading Looks Off
Sometimes the first number sits outside expectations because of scalp swelling, hair braids under the tape, or a squirmy baby. A calm recheck with careful tape placement often moves the dot to a more expected spot. When the dot stays far from the rest of the growth picture, your team may measure parents’ head sizes, ask about family head size patterns, and plan a short-term follow-up.
Practical Notes From The Nursery
- Measure on dry hair and smooth the tape so it lies flat on skin.
- Keep your baby’s gaze forward; head tilt can shave millimeters off the loop.
- Take a photo of the tape position the first time so you can copy it later.
- Store your numbers in one place: a baby book, an app, or your phone notes.
Recap And Next Steps
Most term newborns measure near 34 cm around, with normal living space from the low 30s to the mid 30s. Good readings depend on correct tape placement and repeat checks. Plot results on trusted charts, watch the trend, and ask your care team whenever something seems off. That partnership keeps the numbers meaningful.