For reference: I upsized these on purpose, and they worked fine for me. My foot measures exactly 45 on the Brannock device. I wear 45 in the LS Baltoro 2.0, 45 in Scarpa ice boots, 44 in Birkenstocks, 11 in Chaco, 46 in most running shoes, 41.5 Mythos (nuts, huh?), UK 10 in Blundstones, 44.5 in Shimano road shoes, 45 in Sidi MTB shoes, etc. I'd say the Spantiks are pretty much true to size.