I had originally purchased a pair of Acorn Blairs in a size UK 9. I was a little apprehensive as that seemed small for my generally 11-11.5 US feet but the size guide recommended a 9 as I measured my foot. Those ended up being too tight and just didn’t stretch/break in as I hoped. I eventually had to admit defeat And order a size UK 10 and it was perfect. Maybe my feet are a little wider than the 002 last so I needed to go up a size but these fit like a dream and I’ll continue to get size 10 from now on. Luckily a friend ended up being a size UK 9 and he loved them so the smaller shoes still found a good home.