The most common hat size for women is a S/M (57cm). If you consider yourself to have a "small head" we suggest going with size 55cm.
Camp The Label Beanies are sized as follows
Infant - Avg for babies age newborn-3 years old
Youth - Avg. for children 3-5
Adult Small/Med. - Suggested for those with head circumference of 55-57cm
Adult Large/XL - Suggested for those with a head circumference of 58+
NOTE: To wear "fisherman style" aka double folded, please size up.