Baby Head Circumference: Percentile Chart by Month, How to Measure and When to Worry

Baby head circumference is the measurement around the widest part of your baby’s head, and on the WHO standards the median is about 34.5 cm for boys and 33.9 cm for girls at birth, growing about 12 cm in the first year.

Your pediatrician measures baby head circumference at almost every well-baby visit because head growth reflects brain growth. A number on its own rarely means much. What your doctor watches is whether your baby keeps following a steady curve.

This guide covers how the measurement is taken, a month-by-month chart taken straight from the WHO tables for boys and girls, what head circumference percentile means, how family head size and prematurity change the picture, and which signs mean you should call.

Baby Head Circumference: The Short Answer

A head on the large or small side of the chart is often normal, especially when it has stayed on the same curve since birth and runs in the family. A head that suddenly speeds up or slows down, crossing percentile lines, is what gets a closer look.

Why Pediatricians Track Head Circumference

Your baby’s head grows because their brain is growing. The American Academy of Pediatrics (AAP) explains on HealthyChildren.org that doctors watch for changes in head circumference in infancy because it helps show whether the brain is growing as expected.

That is why the measurement is taken over and over. The StatPearls clinical review on macrocephaly, published by the National Institutes of Health (NIH) on its NCBI Bookshelf, says serial measurements at each health supervision visit remain necessary through 24 to 36 months of age. A series of readings shows how fast the head is growing, which is more useful than any one number.

Head size is read together with weight, length and developmental milestones. For weight, our average baby weight by month guide uses the same WHO charts.

How to Measure Baby Head Circumference

In the clinic this measurement is called the occipitofrontal circumference (OFC). StatPearls describes the technique: a flexible tape placed just above the eyebrows in front and around the most prominent part of the back of the head, so you capture the widest loop.

• Use the right tape: a soft, flexible measuring tape (the kind used for sewing), not a rigid ruler or a metal tape.
• Find the front point: lay the tape across the forehead just above the eyebrows.
• Find the back point: bring the tape around to the fullest, most rounded part of the back of the head.
• Keep it level and snug: the tape should lie flat against the head, not twisted, and firm enough to press down the hair without squeezing.
• Measure more than once: slide the tape slightly up and down at the back and keep the largest reading. Measure two or three times and see whether the numbers agree.

Small errors are easy at home. A wiggly baby, thick hair or a tape sitting a little low can shift the result by about a centimeter, roughly a month of head growth after 3 months. If a home number seems off, let your pediatrician re-measure.

Right after birth, the Centers for Disease Control and Prevention (CDC) notes, a provider may wait to measure if delivery may have changed the shape of the head.

Baby Head Circumference Chart by Month (WHO Standards)

In the United States, the CDC recommends using the World Health Organization (WHO) Growth Standard Charts for children from birth to 2 years, and the CDC growth charts from age 2 on. The CDC explains that the WHO standard shows how infants should grow in healthy, well-supported environments (the study included U.S. children), and recommends it whether a baby is breastfed or formula fed.

The tables below are copied from the WHO head circumference-for-age percentile tables. The 50th percentile is the median. The 3rd and 97th percentiles mark the outer edges of the usual range on the WHO tables; about 3 in 100 healthy babies measure below the 3rd and about 3 in 100 above the 97th.

This chart is a reference, not a diagnosis. A baby outside these numbers is not automatically unwell, and a baby inside them is not automatically fine. Your pediatrician plots the exact measurement for your baby’s exact age (or corrected age) and sex, and looks at the trend across visits.

What Head Circumference Percentile Means

A head circumference percentile compares your baby with healthy babies of the same sex and age. At the 75th percentile, your baby’s head is larger than about 75 of 100 of them.

• Higher is not better: the AAP says on HealthyChildren.org that coming in at the 10th percentile is no better or worse than coming in at the 90th.
• The trend matters most: the AAP puts it plainly: what pediatricians care about most is the trend in weight, height or head circumference, and one point on a chart is not as useful as several points over time.
• Crossing lines gets attention: StatPearls says further evaluation is warranted when serial measurements cross one or more major percentile lines, for example a head that moves from the 25th up past the 75th, or from the 50th down past the 10th.
• Clinical cutoffs vary: the CDC explains that cutoffs used on the WHO charts correspond to the 2.3rd and 97.7th percentiles, labeled the 2nd and 98th on the WHO charts. That is why you may hear slightly different numbers from different sources.

How Fast a Baby’s Head Grows in the First Year

Head growth is fastest right after birth and slows through the first year. StatPearls gives these typical rates of head circumference growth:

The WHO medians show the same slowdown: a boy at the median goes from 34.5 cm at birth to 46.1 cm at 12 months, then gains only about 2.2 cm over the whole second year.

StatPearls also flags a rapid change: a head that grows more than 2 cm within one month in a baby under 6 months warrants further evaluation. Head growth can come in uneven steps, much like baby growth spurts in weight, which is another reason one measurement on its own is not the whole picture.

Family Head Size, Head Shape and Other Things That Affect the Number

Big and small heads run in families. StatPearls notes that family members commonly share larger-than-average head sizes, and describes benign familial macrocephaly: a large head that runs in the family, with a growth curve that stays parallel to the upper percentile lines, in a child who is developing normally. For a baby like this, your pediatrician may measure your head and your partner’s head and compare them with reference curves (sometimes called Weaver curves).

• Parents’ heads: if one or both parents have large or small heads, a baby on the high or low end of the chart is less surprising.
• Head shape: StatPearls describes plagiocephaly as flattening of one region of the skull, which commonly occurs with prolonged positioning of the head in one direction. A flat spot is a shape question, separate from overall head size. Our baby soft spot guide covers flat spots and head shape, and tummy time by age shows how to vary your baby’s position while awake.

For safe sleep, always place your baby on their back on a firm, flat, bare surface, even if you are worried about a flat spot. Head shape is managed with awake time and position changes, never with pillows, wedges or positioners in the sleep space.

Premature Babies and Corrected Age

Compared with full-term babies of the same age, a preemie’s head can look small when it is growing just right. That is where corrected age (adjusted age) comes in. HealthyChildren.org explains the math: subtract the baby’s gestational age at birth from 40 to find how many weeks early the baby was born, then subtract those weeks from the baby’s actual age. Its example: a baby born at 32 weeks was 8 weeks early, so at 16 weeks old her corrected age is 2 months. The AAP says corrected age gives a better picture during roughly the first two years.

The CDC adds that providers can assess a newborn’s head size on charts that account for the length of pregnancy (INTERGROWTH 21st), as well as on WHO charts for ages 0 to 2. StatPearls says frequent head monitoring is especially important in high-risk groups, including preterm infants. If your baby spent time in the hospital after birth, our NICU baby guide covers corrected age and follow-up care, and you can ask your pediatrician which age they are using when they plot your baby’s measurements.

Big Head Baby (Macrocephaly): When It Is a Concern

Macrocephaly means a head circumference more than 2 standard deviations above the mean for age and sex, roughly at or above the 97th percentile, according to StatPearls, which estimates it affects about 2% to 3% of the population. StatPearls says macrocephaly by itself is often benign in a baby with otherwise normal growth, development and neurologic exam.

Common explanations StatPearls describes include:

• Benign familial macrocephaly: a large head that runs in the family and follows its own steady curve.
• Benign enlargement of the subarachnoid spaces: extra fluid around the brain that usually appears in the first 6 months, is more common in boys and typically comes with normal development.
• Hydrocephalus: a buildup of fluid inside the skull, which needs prompt medical care.

According to StatPearls, a large head deserves a closer look when it measures above the 97th percentile, crosses major percentile lines, or grows more than 2 cm in a month in a baby under 6 months, and especially when it comes with symptoms such as lethargy, irritability, vomiting, developmental delay or eyes that have trouble looking up. A soft spot that stays tense and bulging when your baby is calm and upright is also a reason to seek care; see when a bulging soft spot is an emergency.

Small Head Baby (Microcephaly): When It Is a Concern

The CDC describes microcephaly as a condition where a baby’s head is much smaller than expected. It can range from mild to severe and can occur alone or with other birth defects. A head that is simply on the small side of the chart, growing along its own curve in a baby who is meeting milestones, is a different situation from microcephaly.

According to the CDC, in most babies with microcephaly the cause is unknown. Known causes include certain infections during pregnancy (such as Zika, toxoplasmosis or cytomegalovirus), malnutrition before or after birth, exposure to alcohol or certain drugs during pregnancy, and problems with blood supply to the baby’s brain during development.

Depending on severity, the CDC says microcephaly can come with seizures, developmental delay, intellectual disability, feeding difficulties, and hearing or vision problems. Babies with mild microcephaly often have no other problems but need regular checkups.

A small head gets a closer look when it falls well below the usual range, when it slows down and drops across percentile lines, or when it comes with feeding trouble, seizures, or delays in skills like head control and other monthly milestones.

What Your Pediatrician May Do Next

If your baby’s head is outside the usual range or has changed course, the first step is usually to measure again and look at the whole chart.

• Repeat and compare: re-measure, plot it, follow the curve, and measure parents’ heads (StatPearls).
• Full exam: check the soft spot, development and neurologic exam.
• Head ultrasound: while the soft spot is still open, StatPearls describes ultrasound as a low-cost first imaging option.
• CT or MRI: StatPearls notes CT is fast but uses radiation, and MRI shows more detail without radiation but often needs sedation. The CDC notes MRI may be ordered if microcephaly is suspected.
• Referral: depending on findings, a pediatric neurologist, neurosurgeon, geneticist or developmental pediatrician (StatPearls). For babies with microcephaly, the CDC notes early intervention services such as speech, occupational and physical therapy can help.

Good questions to ask: Which percentile is my baby on, and has it changed? Are you using corrected age? Should you measure our heads?

Related Betteroo Guides

• Average Baby Weight
• Baby Soft Spot
• Baby Milestones By Month
• Baby Growth Spurts
• When Can Babies Hold Their Head Up
• NICU Baby

When to Call Your Pediatrician

Call 911 or go to the emergency room right away if your baby:

• Has a truly bulging soft spot: one that stays tense and raised when your baby is calm and upright, especially with fever, vomiting or unusual drowsiness. MedlinePlus says a truly bulging fontanelle needs immediate emergency care.
• Has a seizure: stiffening, jerking, or staring spells with unresponsiveness.
• Is very hard to wake or unusually limp: or is lethargic and not acting like themselves, particularly with repeated vomiting.

Call your pediatrician’s office (same day or next available) if:

• Your baby’s head seems to be growing very fast, or your home measurements show a big jump between visits.
• Your baby’s head has dropped or jumped across percentile lines on their growth chart.
• Your baby is unusually irritable, is feeding poorly, or keeps vomiting.
• Your baby’s eyes seem to have trouble looking up, or seem fixed downward.
• Your baby is losing skills or falling behind on milestones.
• You notice a flat spot, an unusual head shape, or a soft spot that seems to be closing very early or staying very large.

If you are not sure, call. A quick re-measure at the office is easy and usually reassuring. This article is general education, not medical advice, and it cannot replace an exam by your baby’s doctor.

Frequently Asked Questions