To measure head circumference accurately, wrap a flexible, non-stretchable measuring tape around the widest part of the head, passing just above the eyebrows in front and over the most prominent bump at the back of the skull. The goal is to capture the largest possible circumference. This measurement is a routine part of pediatric checkups and occasionally useful in adults, and getting it right at home takes just a minute once you know the landmarks.
Equipment You Need
The single most important detail is using the right tape. A fabric sewing tape will stretch slightly with tension and give you an inaccurate reading. Use a flexible but non-stretchable measuring tape, ideally a plastic one where one end inserts into the other so it locks in place. These are the same tapes used in pediatric clinics. You can find them online or at medical supply stores for a few dollars. If you don’t have one, a piece of non-stretchy string wrapped around the head and then measured flat against a rigid ruler works in a pinch, though it’s less precise.
Step-by-Step Technique
Have the person sit or lie comfortably. For infants, laying them on their back or holding them in your lap works well. Remove any hats, hair clips, or thick hairstyles that would push the tape away from the skull. You want the tape resting against the skin or as close to it as possible.
Place the tape across the forehead, just above the eyebrow ridges. This bony ridge above the eyes is your front landmark. Now wrap the tape around the head at the same level on both sides, bringing it over the most prominent point at the back of the skull. You can feel this bump by running your fingers along the back of the head. The tape should sit at the same horizontal level all the way around, not riding up on one side or dipping down on the other.
Pull the tape snug but not tight. It should compress any hair without pressing into the skin. Read the measurement where the tape overlaps, to the nearest millimeter (or sixteenth of an inch). Then do it again. Take at least two, ideally three, separate measurements and use the largest one. Even trained clinicians see variability of over a centimeter between readings, so repeating the measurement is not optional if you want accuracy. A study comparing tape measurements on infant heads found that precision varied by about 1.6 cm across repeated readings, which is enough to shift a baby from one percentile range to another.
Common Mistakes That Skew Results
The most frequent error is placing the tape too high on the forehead or too low at the back. If the tape sits on top of the forehead rather than across the brow ridge, you’ll underestimate the circumference. Similarly, if the tape slips down to the neck at the back, the reading will be too small. Thick or braided hair can add several millimeters. Part the hair to lay the tape flat against the scalp whenever possible.
Another common issue is inconsistent tension. Pulling too hard compresses soft tissue (especially on infants with open fontanelles) and gives a falsely small number. Barely touching the head gives a falsely large one. Aim for firm contact without visible skin indentation.
When and Why Head Circumference Is Measured
Pediatricians measure head circumference at every well-child visit from birth through at least 24 months. The World Health Organization publishes separate growth charts for boys and girls covering birth to five years, plotting circumference against age. In the United States, the CDC recommends using WHO growth standards for children under two.
The measurement itself is less important than the trend. A single reading tells you whether the head is relatively large or small for age, but what matters more is whether the growth curve follows a consistent trajectory over time. A head that has always tracked along the 10th percentile is perfectly normal. A head that jumps from the 25th to the 90th percentile in two months signals something worth investigating.
What the Percentiles Mean
The WHO defines abnormal head size as anything beyond 2 standard deviations from the mean, which corresponds roughly to below the 2nd percentile or above the 98th percentile. A measurement below the 2nd percentile is classified as microcephaly (an unusually small head), and above the 98th percentile as macrocephaly (an unusually large head). Both can be completely benign, especially if a parent’s head is similarly sized, or they can indicate conditions that need evaluation.
For adults, the thresholds are defined by absolute numbers rather than age-based charts since head growth is essentially complete. Research on adult populations found that men with a circumference above 60 cm and women above 58 cm fall into the macrocephalic range. Microcephaly thresholds were 53.6 cm for men and 51.3 cm for women. Adult head circumference is rarely measured in routine care but becomes relevant in diagnosing conditions involving fluid buildup in the brain or elevated pressure inside the skull.
Limitations With Unusual Head Shapes
Head circumference assumes a roughly typical skull shape. When that shape is altered, the number can be misleading. In craniosynostosis, a condition where one or more skull plates fuse too early, the skull compensates by growing in other directions. The result is a head that looks obviously misshapen but often measures within the normal circumference range. Research published in Arquivos Brasileiros de Neurocirurgia found that most children with confirmed craniosynostosis had a statistically normal head circumference, because the skull compensated with growth in other dimensions. The measurement captured a normal perimeter around a distinctly abnormal shape.
Similarly, positional plagiocephaly (a flat spot from sleeping position) changes the shape without necessarily changing the circumference. In these cases, other measurements like the distance from front to back or ear to ear are more diagnostically useful than circumference alone. If you’re tracking head shape rather than size, circumference alone won’t give you the full picture.
Measuring at Home vs. the Clinic
There’s nothing wrong with measuring at home, and many parents find it reassuring to track growth between appointments. Use the same tape each time, measure in the same conditions (before or after a feeding matters less than consistency), and write down the date, age, and measurement. You can plot the results on the WHO growth charts available free on their website, with separate charts for boys and girls.
Keep in mind that your home readings may differ slightly from the clinic’s. Variation of a few millimeters between measurers is normal. What you’re looking for at home is the overall pattern: steady growth along a curve, not necessarily matching the exact number your pediatrician recorded. If you notice the circumference plateauing for weeks or jumping dramatically, that’s useful information to bring to the next visit.