How to Measure Your Baby’s Head Circumference

The distance around a person’s head is known as their head circumference.  When it comes to monitoring baby and child growth, head circumference is one of 3 key measurements.  Height and weight are the other two.  Head circumference in infancy is particular important because it is related to the growth of the brain.

You might think it would be easy to measure circumference.  It’s not.  Imagine measuring the distance around a volleyball with a tape or string.  You’ll get it right if you can do so at the equator of the ball. If your string slides up or down, your reading will be too low.

A person’s head is more difficult to measure than a ball because a head is lumpy and far from spherical.  Exactly where should you put the tape or string?  Measuring a baby can be even harder because they are apt to move and push the string away.  Never fear, here’s how to do it.


  • Non-stretchable lace or piece of string that is at least 1 m (1 yard) long;
  • measuring tape, yard stick, or a meter stick;
  • paper and pencil;
  • helper (this is a 2-person job);
  • and, most crucially, a baby.

Step-by-step instructions

First, make sure that your baby has no items on his or her head that may interfere with the measurements, such as braids, barrettes, or ribbons.  Review the following video and record the length measurement in centimeters or inches on the paper.  If possible, record fractional parts of your unit of measurement.  If possible, switch places with your partner and have them take their own reading (without knowing your reading).  Compare the two readings.  It is likely that they differ.  If so, calculate the average of the two (an average is more reliable than either single reading).

Compare to WHO norms

Once you have your baby’s reading, you can compare it to the World Health Organization norms.  An easy way to do this is to use the following Baby Growth Calculator.  There you will enter your baby’s gender, birth date, measurement date, measurement unit (inches or centimeters), and your length value.  As the shown below, the Calculator will determine your child’s age in months and head circumference percentile.

Do not treat the percentile result like a school grade.  A higher percentile is not better than a lower percentile.  Healthy babies can differ greatly in head size, and head circumference percentiles are a numerical way of describing them.  Many factors can influence your baby’s head size.  For example, a baby born prematurely will have a smaller head size at 1 month of age than will a baby who was born a week after the due date.  However, an extremely small (<3%) or large (>97%) percentile may be a sign of developmental difficulty.  If this is the case for your baby, you should consult a health care professional.

a good source on how to interpret the percentiles.