I think they fit so differently that the specific shoe needs to always be tried on. I am a UK 7.5 to 8 (which according to the UK shoe size guides is a 41.5 to 42 euro or a 10.5 to 11 US) but I always wear a 41 in Chanel apart from quilted ballerinas (41.5) and thong sandals (42)
I totally agree. I'm an 11 in sneakers and everything under the sun from 10/40 to 11/41 in every designer and style of shoe, and in Chanel I go up to a 42. I have narrow feet and no arches, too.
For instance:
I have a pair of thong sandals that are a 42 and are probably a little/tiny bit too big, but they were on super-sale at Bloomie's, so oh well!
I also have platform booties (chain on the platform), and I had to literally "pop" a 40.5 onto my feet when I was trying on the patent captoe, which I loved, but they would have killed me, especially since I pretty much never wear heels (though these aren't too bad, despite the stiletto heel). My other choice (sale again -- always!) was a 42, and they're a good fit, especially with an insole, which I also always wear because I have flat feet.
I have this past season's chunky heel loafers (posted in "Chanels in action" and "January finds") and I found those in a 41. They fit well, maybe a little big in the heel because I have very narrow feet and heels. I could have probably gone for a 41.5, and I just remembered that maybe I should have asked the cobbler to stretch them when I was there with them today to get rubber on the bottom, but they don't hurt and they'll stretch with wear! I can also always get them stretched later.
I bought this past season's beautiful flat, elephant grey booties, and a 42 is PERFECT. I had wanted the chunky heeled red ones. The only ones left were a 40.5, and they were WAY too small.
I also have the shimmery black moccasins in a 41, and they fit, but I'm really still debating them and kept forgetting to call around and see if anyone had a 41.5 or 42 to compare. I feel like maybe they'd start bugging me if I wear them for a while, because they're ever-so-slightly tight. I had no black shoes, but then I found these, buttery Ferragamo loafers, and Gucci studded ones on sale at the same time. I like these, and who doesn't want another pair of Chanels, but they were obviously more expensive, and they're not as practical as the other two, which also fit better.
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Oh, I realized I took some quick pictures to show my mom some things before I went to visit last month, so sorry they're not great or anything, but here are the shoes I'm talking about!
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There have been some Chanel loafers/ballerinas that I have tried on that have been like flip flops in a 42. But that happens with all brands. Two pairs of my Ferragamo mocs are 11s, one are a 10 (they didn't make 11 in those, grr.). One Varina is a 10 and I could have stood a 10.5. Another is a 10 and they're perfect; the 11 was so gigantic, it was ridiculous. The last, a 10 and 10.5 were the same. I have one pair of Weitzman dress sandals that were SO big in a 10 that I went down to a 9.5 and even those are big, which is crazy for someone who averages out pretty well to a solid 11.
So you really can't say "I'm always this in X shoe," except for sneakers, I'd say. I'm always an 11 in New Balance, no ifs, ands, or butts!