If you want to make knitted or crocheted hats as gift you don’t always know the size of the head of the recipient. For the average head sizes in the list she made an empirical study and in case of need it may help you.
But of course it’s always better to measure ;-)
Links:
Average Head Sizes (Sizing Information)
Here at unikatissima:
Entries with the tag ‘knitting’
Entries with the tag ‘crochet’
Entries with the tag ‘hat’