The Rule of 3's and 9's
This rule is an easy way to remember the 50th percentile for head circumference.
Just remember that a full term infant's head circumference is about 30
centimeters, then add 5 cm for every 3 or 9 birthday
| Age |
H.C. (cm) |
| Birth |
30 |
| 3 months |
35 |
| 9 months |
40 |
| 3 years |
45 |
| 9 years |
50 |
| Adult |
55 |
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