CDC/NCHS Infant Head Circumference for Age Percentiles (<36 months)
Calculate Z-score and percentile
This tool is based on data from the Centers for Disease Control (CDC) Growth Charts released in 2000. The CDC growth charts are recommended for use in clinical practice and research to assess size and growth in U.S. infants, children, and adolescents.
- Microcephaly is a Head Circumference greater than two standard deviations below the mean.
- Macrocephaly is a Head Circumference greater than two standard deviations above the mean.
- At the extremes (>97th percentile or <3rd percentile), small differences in percentiles represent clinically important differences in head circumference. At these extremes, the z-score is a more precise reflection of how far the measurement deviates from the mean, and is a useful tool for tracking changes.