I normally wear a size 8 and I ordered the 38.  I love these slippers so much.  I meant to have them just around the house but some times they are so comfy I just end up wearing them on errands too.  The wool is not scratchy and keep my feet warm so much that I will not be wearing these in summer.  They replaced my UGG slippers which kept my feet warm from my cold hardwood floors in winter, but these are an improvement because they have arch support,  They are the worth the money, if they hold up.