I already have many shoes of this brand... normally I wear 6.5 US (M) for loafers (= 37FR size). For other shoes I may fit on 36.5FR. With theese boots, I ordered 6.5US (M), but after a while, I think 6 US(M) would fit better. I can wear it with thick winter socks. I give 5 stars because though there is no zip, it is easy to wear. It fits the muscular calf. I had experience to wear it all day long, and the next day, I was fine. No ache at all. I do recommand.