How Big Is The Average Newborn Head? | Quick Size Guide

Average Head Size At Birth (What The Numbers Say)

Across term deliveries, head circumference tends to sit near the mid-30s in centimeters. Boys run a tiny bit larger than girls. The figures below come from the WHO head circumference standards and show birth percentiles. If your baby lands anywhere inside this band, that usually reflects normal variation.

Percentile	Boys (cm/in)	Girls (cm/in)
5th	32.4 cm (12.8 in)	31.9 cm (12.6 in)
15th	33.1 cm (13.0 in)	32.7 cm (12.9 in)
25th	33.6 cm (13.2 in)	33.1 cm (13.0 in)
50th	34.5 cm (13.6 in)	33.9 cm (13.3 in)
75th	35.3 cm (13.9 in)	34.7 cm (13.7 in)
85th	35.8 cm (14.1 in)	35.1 cm (13.8 in)
95th	36.6 cm (14.4 in)	35.8 cm (14.1 in)

A quick rule of thumb: the middle of the curve sits at roughly 34–35 cm, or around 13½–14 inches. Tape placement matters, so proper technique helps the number mean something.

Can A Newborn’s Head Look Bigger Or Smaller Right After Birth?

Right after labor, heads can look cone-shaped or puffy. That’s molding and temporary swelling from the trip through the birth canal. Both usually settle within a few days as fluid shifts and the skull bones relax back into place. Because of this, teams often take the official measurement after the first day.

Birth method can nudge the reading too. Vacuums and forceps may leave identifiable swellings that sit above the skull and can bump a tape by a few millimeters. These changes fade, and the true circumference becomes clearer on repeat checks.

How Newborn Head Size Is Measured Correctly

Clinicians measure the occipito-frontal circumference (OFC) — the widest loop around the head. The tape passes just above the eyebrows and ears, then around the most prominent point at the back of the skull. Two or three attempts are common; the largest consistent value is recorded to the nearest millimeter.

Soft spots, hair, and bandages can throw things off. The tape should sit flat on skin, not ride up. If swelling sits on top of the skull, staff avoid compressing it, note the finding, and re-check as it resolves.

Average Head Size Of A Newborn: Normal Range & Context

Biology brings range. Gestational age affects size — late-preterm babies tend to have smaller heads than those born at forty weeks, while post-term babies trend larger. Parental head size matters too; big-headed families often have big-headed babies.

Clinicians look at the whole picture: length, weight, and the head curve together. A head below the third percentile or above the ninety-seventh can prompt a closer look, yet many babies outside the middle band are perfectly healthy when growth tracks steadily.

How Clinicians Read Percentiles And Z-Scores

Percentiles rank a baby against a large reference group. At the fiftieth percentile, half the babies in the reference sample measure smaller and half larger. A z-score says the same thing using standard deviations. The center of the chart is zero; +1 sits about one channel above the middle, −1 one channel below.

Neither tool labels a baby as healthy or not on its own. What matters is a steady track that follows a curve over time. A baby who lives at the tenth percentile month after month can be growing just as well as a baby at the ninetieth.

Premature And Post-Term Birth: What’s Typical

Babies who arrive early often have smaller heads at first because the last weeks of pregnancy bring rapid brain growth. Teams caring for preterm infants use charts based on gestational age at birth, such as the INTERGROWTH-21st newborn standards, to judge size on day one. As weeks pass, many preterm babies catch up on head growth, especially once feeding is established.

At the other end, a baby born after forty weeks may post a bigger number. That doesn’t tell you anything about future height or school performance; it simply reflects timing. Once babies reach their due-date window, your pediatric office switches to postnatal charts like the WHO standards all infants use.

For babies who needed intensive care or had bleeding under the scalp at birth, staff may check head size more often in the early days. Extra data points help separate temporary changes from true growth.

Head Growth After Birth: What To Expect

Head circumference expands briskly in infancy. On average, it increases about 1 cm per month across the first year, with the pace livelier in the early months. By the first birthday, most infants sit at roughly three-quarters of adult brain size. That’s why regular plotting on a growth chart matters — patterns tell the story, not a single dot.

You’ll see small ups and downs from visit to visit. The plot should form a smooth line that follows a percentile channel over time. A sudden jump across several channels or a steady slide downward deserves attention, especially if paired with symptoms such as vomiting, a bulging soft spot, lethargy, or poor feeding. If any of those show up, call your pediatrician’s office without delay.

Use this quick conversion table if your tape reads in centimeters but your baby hats list inches.

Most clinics plot head size at each newborn and infant visit along with length and weight. Keeping the same tape placement every time reduces noise and makes trends easier to see. If a number looks off compared with prior points, teams often repeat the measure, then rely on the shape of the curve to guide decisions.

Head Size Myths You Can Ignore

If a lamp throws shade on your tape reading — stray hair or a fussy baby — take a break and try again later. One calm pass beats three rushed ones.

• “A big head means a smarter kid.” Head size tracks skull growth, not talent or potential.
• “A small head always signals trouble.” Many healthy children sit near the lower curves and thrive.
• “Hats shape the head.” Head shape comes from bones and sutures, not beanies.
• “You can’t measure this at home.” You can collect a solid number with a soft tape and good placement.

Headwear, Car Seats, And Everyday Fit

Newborn hats list sizes in inches or by labels like “newborn,” “0–3 months,” or simple S/M/L. Since most term heads fall near 13½–14 inches on day one, beanies marked for newborns usually work. If a hat leaves a deep mark, pick a looser knit or a size up. Warmth matters more than snugness at this stage.

Car seat straps should sit at or just below shoulder level for rear-facing seats. Head size rarely changes strap placement, but extra inserts and padded headrests that didn’t come with the seat can cause poor fit. Stick with the pieces included by the manufacturer and follow the manual.

When To Get Medical Advice

Reach out to your child’s clinician if any of the following happens:

• The head curve crosses two major percentile lines between visits.
• The soft spot bulges or looks sunken, or head shape changes quickly.
• Feeding troubles, repeated vomiting, unusual sleepiness, or seizures appear.
• You notice a fast-growing swelling on the head or a new bruise without an injury you can explain.

Family history can guide next steps. If parents or siblings have larger-than-average heads, a baby with a high percentile might simply share the same trait. Measuring parents’ head sizes at home with a soft tape can be helpful information to bring to the visit.

Tips For Parents Measuring At Home

1. Use a flexible, non-stretch tape. If you only have a ribbon or string, mark it and compare against a ruler.
2. Find the biggest loop: eyebrows and ears in front, the bump on the back of the head behind.
3. Take three readings and use the largest one that repeats.
4. Write the date and value, then plot it on the same chart used at checkups.

If the number looks far off from your baby’s usual channel, repeat the measurement later the same day. Babies wiggle; small placement shifts can change the reading by a few millimeters. Try again at home.

Centimeters	Inches	Notes
31 cm	12.2 in	Smaller than typical term
32 cm	12.6 in	Within common range
33 cm	13.0 in	Within common range
34 cm	13.4 in	Near average
35 cm	13.8 in	Near average
36 cm	14.2 in	Larger than typical term
37 cm	14.6 in	Larger than typical term

What Shapes Head Size At Birth

Several factors steer the number you see on day one:

• Gestational age: each extra week in the third trimester adds a little more head growth.
• Placental health and prenatal nutrition: steady oxygen and nutrients support steady brain growth.
• Multiple birth: twins and triplets are often smaller at birth, including head size.
• Fetal position and labor length: molding changes shape temporarily without changing skull volume.

Key Takeaways For New Parents

• Most term newborns measure near 34–35 cm around the head.
• Percentiles mark position in the crowd, not a grade.
• Growth patterns over time matter more than a single point.
• When something doesn’t fit the pattern, your pediatric care team wants to hear from you.

For extra reading on head size charts and expected growth, see the Merck Manual overview.