head circumference

Hi mga mommies.. I was a bit concern with my little ones head kasi it looks small to me.. She just turned 4 months nung 16 and her head circumference is 15.5 inches.. Ano po ba ang normal head circumference ng mga babies?.. When i am google searching panay microcephaly nalabas kya natatakot ako.. Her pedia appointment is on her 6th months pa.. Thank u in advance po sa sasagot