Work out head circumference percentile instantly with clear inputs, formula shown and shareable results.
Occipitofrontal circumference is standardised as a z-score against the reference mean and standard deviation for age, then read off the normal curve as a centile. Head circumference is charted in the first years because it tracks brain growth, and the plus or minus 2 SD band is the usual trigger for a closer look.
Z-score
z = (measured circumference - reference mean) / reference standard deviation
Centile
centile = normal cumulative distribution of z x 100
z = (measured circumference - reference mean) / reference standard deviation. Occipitofrontal circumference is standardised as a z-score against the reference mean and standard deviation for age, then read off the normal curve as a centile.
Head circumference is charted in the first years because it tracks brain growth, and the plus or minus 2 SD band is the usual trigger for a closer look.
Enter head circumference, reference mean for age, reference standard deviation. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.