To measure your baby’s head circumference, wrap a non-stretchy tape measure around the widest part of the head, passing it over the most prominent point of the forehead (usually one to two finger-widths above the eyebrows) and around the widest part of the back of the skull. The average newborn head measures about 13¾ inches (35 cm) at birth and grows to roughly 15 inches (38 cm) by one month.
What You Need
Use a tape measure that cannot stretch. A flexible metal tape measure works best. Fabric sewing tapes can stretch over time and give you a reading that’s slightly too large. Paper measuring tapes, like those sometimes given at pediatric offices, are another good option since they won’t expand under tension. Avoid elastic or worn-out tapes entirely.
Step-by-Step Technique
Place the tape around the widest possible circumference of your baby’s head. On the front, position it across the most prominent part of the forehead, typically one to two finger-widths above the eyebrows. On the back, find the part of the skull that sticks out the most. The tape should sit above the ears on both sides, not over them.
Pull the tape snug enough to compress the hair against the scalp but not so tight that it digs into the skin. You’re looking for a firm, flat contact all the way around. If your baby has thick or textured hair, press the tape down a bit more to ensure you’re measuring the skull, not the hair.
Here’s the most important part: measure three times, and take the largest number. It’s easy to accidentally get a reading that’s too small if the tape slips or isn’t positioned at the true widest point, but it’s nearly impossible to get an artificially large measurement with a non-stretchy tape. Moving the tape slightly between each attempt helps you find the true maximum circumference.
Common Sources of Error
Several things can throw off your reading. Differences in head shape, hair thickness, and how cooperative your baby is during the process all introduce variability. Tape placement and how tightly you pull it are the two biggest factors you can control. If the tape is angled (higher on one side than the other) or sitting on top of an ear, the number will be off.
For newborns measured within the first 24 hours, the reading can be unreliable. During delivery, the skull bones overlap and the head temporarily molds into an elongated shape. The World Health Organization notes that measurements taken this early are often inaccurate for this reason. If your baby was born vaginally and the head looks a bit cone-shaped, a measurement taken a day or two later will be more representative.
What the Numbers Mean
A single measurement tells you something, but the trend over time tells you much more. At well-child visits, your pediatrician plots head circumference on a growth chart that’s specific to your baby’s sex and age. The WHO provides these charts from birth through age 5, though head circumference is most closely tracked during the first 24 months.
Boys tend to have heads slightly larger than girls, though the average difference at birth is less than half an inch (about 1 cm). What matters most isn’t where your baby falls on the chart at a single visit but whether the growth curve stays on a consistent trajectory. A baby who’s been tracking along the 25th percentile and stays there is growing normally. A baby whose measurements suddenly jump to a much higher or lower percentile warrants a closer look.
The American Academy of Pediatrics and CDC use the 2nd and 98th percentiles on the WHO growth curves (corresponding to 2 standard deviations below and above the median) as flags for potentially abnormal growth. Falling below the 2nd percentile may indicate the head is unusually small, while tracking above the 98th may indicate it’s unusually large. Neither is automatically a diagnosis. Many babies outside those lines are perfectly healthy, but the pattern prompts further evaluation.
How Often to Measure
During the first year, head circumference is typically checked at every well-child visit. The WHO growth velocity charts use two- and three-month intervals for babies up to 12 months, and four- to six-month intervals from 12 to 24 months. This means your pediatrician isn’t just looking at the size of your baby’s head at each visit but also calculating how fast it’s growing between visits.
At home, you don’t need to measure weekly. Checking once a month during the first year is plenty if you want to track growth between appointments. More frequent measurements introduce more noise than signal, since small technique differences can make it look like growth has stalled or jumped when it hasn’t.
Why Head Size Matters in Infancy
A baby’s skull is designed to expand. The bones haven’t fused yet, and the soft spots (fontanelles) and the seams between skull plates (sutures) allow the head to grow as the brain grows. Most sutures stay open until brain growth slows in the second year of life, and the front soft spot typically closes around that time too. Once a suture fuses, growth perpendicular to that seam stops. That’s why tracking head circumference early matters: it’s an indirect measure of whether the brain has room to grow at a healthy pace.
Research shows a strong relationship between head circumference and fontanelle size in newborns. Larger heads tend to have larger fontanelles, and both measurements serve as indicators of normal cranial development. The two are typically assessed together during routine exams in the first two years.
Premature Babies
If your baby was born before 37 weeks, standard WHO growth charts don’t apply right away. Preterm infants are assessed against fetal growth patterns using specialized charts, the most well-known being the Fenton growth charts. These begin at 22 weeks gestational age and extend to 10 weeks after the due date, at which point the baby transitions to the standard WHO charts.
The latest generation of Fenton charts was built from data on fetuses without growth abnormalities, making them a more accurate target for what healthy preterm growth should look like. One practical consequence: more premature babies will be classified as small for gestational age on these newer charts compared to older versions. If your preemie’s care team mentions the Fenton chart, this is the reference they’re using to evaluate whether growth is on track.
Tips for Measuring at Home
- Choose the right moment. A calm, alert baby is easier to measure than a squirming, hungry one. Right after a feed often works well.
- Use a helper if possible. One person can hold the baby steady while the other wraps and reads the tape.
- Write it down. Record the date, the measurement in centimeters, and which attempt gave the largest number. This makes it easy to share with your pediatrician.
- Don’t panic over a single reading. A measurement that seems off is more likely a technique issue than a growth problem. Remeasuring carefully, aiming for the largest circumference, often brings the number back into the expected range.