Charles David sizing

I get quite confused at to US sizing in correlation to UK/EU sizes. If 7.5 is 38, how can 8 be 39. Surely it would be 38.5.

I buy shoes from the States regulalry and we also have a couple of brands over here that list in US sizes and I know from my own collection that from experience the size guide on US sites are often off by at least 1/2 a size to a whole size.
 
Actually, it's supposed to be like this: 37 = US 7, 38 = US 8, etc. A lot of European brands run small, though. I'm usually a US 8.5 and my Gucci boots are 38.5, but most of my CLs are 39. My Derek Lams are 39.5 but are a bit too big (could have gone with 39 or 38.5). My Prada shoes were TTS, though (38.5). Just depends on the designer.