It depends on which websites you look at. The "size up" advice from American websites never works in my case as I'm a true European size. I found mytheresa to be quite accurate in their sizing estimate for my size.If I'm a 37.5 in Manolo Hangisi and BB... what size should I get in caged rockstud pumps? 38? I keep seeing websites that say to size up.
I'm a 35 for all caged rockstud pumps (could even go down half a size for kitten heels), and Hangisi 35 was half to a full size too large on me. For reference, my feet have average to small width. HTH!