How to measure a baby's head circumference
Head circumference is the largest circumference around the skull and the simplest way to follow a baby's brain growth indirectly. It is measured at birth and at regular check-ups until the age of two. If you measure at home, use a non-stretch tape and follow these steps:
- Measure while your baby is calm, on your lap or lying on their back; remove hats, clips and headbands.
- At the front, place the tape just above the eyebrows, over the most prominent part of the forehead.
- At the back, pass the tape over the most prominent point of the head (the occiput), keeping it above the ears.
- Pull it snug enough to flatten the hair, but not so tight that it presses into the skin.
- Repeat three times and record the largest value to the nearest 0.1 cm.
Home measurements are less precise than clinical ones, and even half a centimetre can shift the percentile noticeably. Treat the result as a guide rather than an exact value, and use the measurement from your baby's check-up where possible.
Head circumference chart (0–24 months)
The table below is calculated from the WHO Child Growth Standards. For each age it gives the 3rd percentile (near the lower limit), the 50th percentile (median) and the 97th percentile (near the upper limit) in centimetres. Girls and boys have separate references; boys' heads are slightly larger on average.
Girls
| Month | 3rd | 50th | 97th |
|---|---|---|---|
| 0 | 31.7 | 33.9 | 36.1 |
| 1 | 34.3 | 36.5 | 38.7 |
| 2 | 36.0 | 38.3 | 40.5 |
| 3 | 37.2 | 39.5 | 41.9 |
| 4 | 38.2 | 40.6 | 43.0 |
| 5 | 39.0 | 41.5 | 43.9 |
| 6 | 39.8 | 42.2 | 44.7 |
| 7 | 40.4 | 42.8 | 45.3 |
| 8 | 40.9 | 43.4 | 45.9 |
| 9 | 41.3 | 43.8 | 46.3 |
| 10 | 41.7 | 44.2 | 46.8 |
| 11 | 42.0 | 44.6 | 47.1 |
| 12 | 42.3 | 44.9 | 47.4 |
| 15 | 43.1 | 45.7 | 48.2 |
| 18 | 43.6 | 46.2 | 48.8 |
| 21 | 44.1 | 46.7 | 49.4 |
| 24 | 44.6 | 47.2 | 49.8 |
Boys
| Month | 3rd | 50th | 97th |
|---|---|---|---|
| 0 | 32.1 | 34.5 | 36.9 |
| 1 | 35.0 | 37.2 | 39.4 |
| 2 | 36.9 | 39.1 | 41.3 |
| 3 | 38.3 | 40.5 | 42.7 |
| 4 | 39.4 | 41.6 | 43.9 |
| 5 | 40.3 | 42.6 | 44.8 |
| 6 | 41.0 | 43.3 | 45.6 |
| 7 | 41.7 | 44.0 | 46.3 |
| 8 | 42.2 | 44.5 | 46.9 |
| 9 | 42.6 | 45.0 | 47.4 |
| 10 | 43.0 | 45.4 | 47.8 |
| 11 | 43.4 | 45.8 | 48.2 |
| 12 | 43.6 | 46.1 | 48.5 |
| 15 | 44.4 | 46.8 | 49.3 |
| 18 | 44.9 | 47.4 | 49.9 |
| 21 | 45.3 | 47.8 | 50.4 |
| 24 | 45.7 | 48.3 | 50.8 |
Values use an average month of 30.44 days and are rounded to one decimal place.
What does percentile mean?
A percentile shows where your baby's measurement sits compared with healthy babies of the same age and sex. The 50th percentile means 50 out of 100 babies have a smaller head and 50 a larger one. The 15th percentile means about 15 out of 100 are smaller — which is entirely normal.
The z-score says the same thing in standard deviations: 0 is the median, −1 to +1 covers about two thirds of babies, and −2 to +2 almost all of them. The calculator uses the WHO LMS method to find the z-score and then the percentile. What matters most is your baby's own curve over time, not a single number.
When is head circumference a concern?
Most babies grow along their own line somewhere between the 3rd and 97th percentiles, influenced by parents' head size, birth weight and prematurity. Talk to your paediatrician if you see:
- A measurement below the 3rd or above the 97th percentile
- Two or more percentile lines crossed, up or down, over successive measurements
- Head growth that stops or is much faster than expected
- A soft spot (fontanelle) that looks clearly bulging, sunken or closed unusually early
- Other concerns about feeding, sleep or developmental milestones
None of these on its own means something is wrong; family traits or measurement differences often explain them. The assessment belongs to the doctor who examines your baby and follows the growth curve over time.
Is head circumference the same as head shape?
No. Head circumference measures the size of the head; head shape describes its proportions and symmetry. A baby with a perfectly normal head circumference can still have one-sided flattening (plagiocephaly) or a flat back of the head (brachycephaly).
Head shape is assessed with measurements such as CVAI and cephalic index from a 3D scan — a tape measure cannot show it. See our treatments page and our article on head shapes in babies, or book an initial assessment if you are concerned.
Frequently asked questions
What is a normal head circumference for a newborn?
According to the WHO standards, the median head circumference at birth is about 33.9 cm for girls and 34.5 cm for boys. Most healthy newborns fall between roughly 31.7–36.1 cm (girls) and 32.1–36.9 cm (boys), the 3rd to 97th percentiles.
How fast does a baby's head grow?
Head growth is fastest in the first three months, at about 2 cm a month on average. It slows to about 1 cm a month at 4–6 months and about 0.5 cm a month from 6 to 12 months. By the first birthday the head is on average 11–12 cm larger than at birth.
How is head circumference assessed in premature babies?
For babies born before 37 weeks, corrected age is used until 24 months: the number of weeks short of 40 is subtracted from the actual age. A 6-month-old born at 32 weeks is plotted roughly as a 4-month-old. Tick “Born prematurely” in the calculator to do this automatically.
The head circumference is normal but the head looks uneven. What should I do?
Size and shape are different things. If you notice flattening or asymmetry, talk to your paediatrician first; repositioning and tummy time often help early on. A marked or worsening asymmetry can be measured with a 3D scan.
This calculator is for information only and does not replace a medical diagnosis or examination. Always make decisions about your baby's growth together with your paediatrician.