I wear an American 5 7/8 hat size. what does this translate into centimeters, and UK fitted hat sizes?

Most hats have both sizes in the hat. For exaply a tag will generally say 7 1/4 and have 58 for cm right underneath that size. Also check under the sweatband. Sometimes they put the sizes under there too

I don't know I think if you look at Google for converting ... Good luck and good hat