Baby head circumference by age: what is normal?

Most babies' heads grow fast and steadily: roughly 2 cm a month for the first three months, about 1 cm a month from three to six months, then around 0.5 cm a month up to a year. Normal covers a wide range, so clinicians watch the pattern over time rather than judging any single number.

What head circumference tells you, and why it is measured

Head circumference (you may see it written as OFC, for occipitofrontal circumference) is the distance around the widest part of your baby's head. It is taken at birth and at most routine checks through the first year or two, and it goes into whichever record your health system uses: the growth charts in your well-child visit notes in the US, the red book (Personal Child Health Record) in the UK, the Rourke Baby Record and provincial charts in Canada, and your state child health record in Australia.

The reason is simple, and nobody ever explains it at the appointment. A baby's skull is not one solid dome. It is several plates of bone separated by flexible seams and soft spots, and it expands because the brain inside it is expanding. Measuring the outside of the head is therefore an indirect, cheap and completely painless way of keeping an eye on brain growth. No scan, nothing for your baby to tolerate beyond ten seconds of a paper tape.

That is why a clinician cares about a number most parents skim past. Weight moves with feeding, teething, illness and a dozen ordinary things. Head circumference moves slowly and predictably, which is what makes a change in it worth noticing.

Average head circumference by age

The table below comes from the World Health Organization Child Growth Standards, the reference used for babies under two in the UK, Australia, Canada and, for the first 24 months, the United States. It shows three of the printed lines: the 3rd percentile, the 50th (the median) and the 97th.

Read them the right way round. A percentile is a comparison with other healthy babies of the same age and sex, not a grade. A baby near the 3rd percentile is not doing worse than a baby near the 97th; both are simply where they are, and around three in every hundred thriving babies sit below the bottom line, because that is what a bottom line is for. If the chart itself is the confusing part, our guide to what growth percentiles mean and how to read a growth chart works through it properly.

Swipe the table sideways to see every column.

Figures from the WHO Child Growth Standards, which describe babies born at term; preterm babies are usually plotted using corrected age or on a chart supplied by their own doctor.

Boys and girls are plotted separately because the figures differ slightly at every age. Two babies born the same day can be a couple of centimetres apart and both be entirely ordinary.

How fast a baby's head actually grows

Rates are often more useful than absolute numbers, because they tell you roughly what to expect between appointments:

• Birth to 3 months: around 2 cm a month, the fastest head growth of your child's entire life.
• 3 to 6 months: about 1 cm a month.
• 6 to 12 months: roughly 0.5 cm a month.
• After the first birthday: considerably slower, only a couple of centimetres spread across the whole second year.

Added up, that is somewhere near 12 cm across the first twelve months and a small fraction of that in the twelve months after.

These are averages, not targets. Growth is not perfectly even week to week, and a check done a fortnight early or late will not land neatly on the arithmetic. What a clinician looks for over several visits is a line that keeps climbing at a sensible slope, not a number hitting a monthly quota.

How the measurement is taken, and how it gets mismeasured

A non-stretch tape (the disposable paper ones used in clinic, not a dressmaker's tape that gives) goes around the head at its widest point: just above the eyebrows, just above the ears, and around the most prominent part at the back. It should sit snug, flat and level the whole way round. Because the widest path is not obvious, the measurement is repeated two or three times and the largest reading is recorded.

It is easier to get wrong than you would think. Half a centimetre or more can come and go because of:

• Thick, bunched or plaited hair, clips, or a hat edge under the tape.
• A squirming, arching or crying baby.
• A tape sitting too low at the back, or slipping over the ears.
• A stretched, twisted or bent tape, or one read at an angle.
• Fresh moulding or swelling in the first days after birth.
• A different person measuring, with a slightly different technique.

Half a centimetre sounds trivial, but at six months it is a whole month's growth. That is the best reason not to panic over one surprising reading. When a number jumps or stalls, the first sensible question is whether it was measured the same way, and repeating it is routine rather than a sign anything is wrong.

Soft spots, moulding and head shape

Newborn heads are rarely round, and very little of it is a problem.

Moulding. During a vaginal birth the skull plates slide and overlap to get through the birth canal, which is precisely what those flexible seams are for. A cone-shaped, elongated or lopsided head straight afterwards is normal and settles over days to a few weeks. Swelling on the scalp from the birth itself also resolves on its own, though it can take longer.

Flattening. It is very common for part of the back or side of the head to flatten in the early months, because babies sleep on their backs (which is the right and safest way for them to sleep) and because most have a favourite side to turn towards. Positional plagiocephaly, as it is called, is a positioning issue rather than a brain issue, and head shape is not a measure of what is happening inside. Raise it early rather than waiting it out: plenty of supervised tummy time while awake, alternating which end of the cot you lay your baby down at, switching the arm you feed from, and giving them reasons to look towards the less favoured side all help most while the skull is at its most malleable. If the flattening is getting worse, or your baby struggles to turn their head both ways, ask your doctor or child health nurse, who can decide whether anything further is needed.

The soft spots. There are two you can usually feel. The small one at the back of the head normally closes by around two to three months. The larger diamond at the front usually closes somewhere between about nine and eighteen months, and a wide spread of timing is normal. A soft spot that is flat, or that rises and falls very gently with your baby's pulse, is doing exactly what it should. It may bulge briefly while your baby cries, strains or lies flat, and settle again once they are picked up.

When a soft spot is not routine: a fontanelle that looks or feels sunken, or one that is bulging and tense while your baby is calm, upright and not crying, needs urgent medical attention that day. Do not wait for the next appointment.

Big heads, small heads and what family has to do with it

Head size runs in families more visibly than most parents realise. A baby whose head sits high on the chart, in a family where hats never fit, is usually just that family's head, and the same is true at the other end. If the measurement has tracked along its own line since birth, a consistently high or low percentile is not the interesting part.

What clinicians actually watch is the shape of that line over time:

• A head moving steadily along roughly the same percentile, wherever that line happens to sit, is the reassuring pattern.
• A head crossing quickly upward through the printed lines, over a few weeks or a couple of visits, gets looked at.
• A head that has effectively stopped growing between visits gets looked at.
• Head growth that has clearly stepped out of line with the way weight and length are going gets looked at.

Getting looked at is not the same as something being wrong. Usually the next step is a repeat measurement a few weeks later, a look back at the birth figure, and a quick measure of both parents' heads. That is often the entire investigation.

Two limits are worth stating plainly. A chart is a comparison and nothing more: it cannot tell you your child is healthy, and neither can this page. Only your own doctor, who can examine your whole baby alongside everything else they know, is in a position to say anything of the kind. And nothing about a head measurement is a reason to change how you feed your baby. Head growth is not something to be fed up or down, so any change to feeds, formula, top-ups or solids belongs with a clinician who knows your child, never with a number on a chart.

When head size genuinely needs checking

Contact your doctor, health visitor, child health nurse or practice promptly if:

• The soft spot at the front is sunken, or bulging and tense while your baby is calm and upright. This one needs urgent, same-day attention.
• Head measurements are crossing rapidly upward through the lines, or have stalled between visits.
• Head growth has moved noticeably out of step with weight and length.
• The head shape is changing quickly, or you can feel a hard ridge along a seam of the skull.
• Flattening on one side is getting worse, or your baby strongly resists turning their head one way.
• Your baby's alertness, head control, feeding or movement changes, or skills they had seem to slip away.
• There is persistent irritability, unusual sleepiness, repeated vomiting, or an unusual high-pitched cry.
• Your baby has taken a knock to the head, or you are uneasy and cannot fully explain why. That last one is a good enough reason on its own.

None of this is a diagnosis or a substitute for advice from someone who has seen your baby. If something has changed between appointments, ask. Repeating the measurement takes ten seconds and costs nothing.