I purchased the wrong size and it was too big, so it's only been tried on. For those who purchase by 11:59 on January 3rd of the New Year, I'll give you a bonus... A kissmark head/hairband! Size O is a Japanese size designation mainly used for sportswear, and it indicates a size one step larger than L. It is generally understood to be about the same size as XL, LL, or 2L. Meaning of size notations: O: Over Large (larger than L) LL / 2L: Twice Large XL: Extra Large (larger than L)