ARUNAMen's and Women's Woollen Himachali Kullu Patti Topi (Black , 8)

How can i calculate the size of 5. 6. 8. And free

This cap can be used by a adult man or this is for only childrens.

Ive tried 8 size but still its small for me. Can i know free size is bigger than size 8 or i cam get size 9 cap??