they are rubber to hold in place, so they will have plenty of give to fit. you just don't want them too large and keep losing them. if i had to guess tho, i'd say a small.
i have lost plenty of slip on ice protection and if you do get that type, i would suggest you get velcro straps to go over your toe section, closest to your leg, in case they try to slip off when walking in snow that likes to grab them.
i have the largest pair for my size 13 boot, but do not like them and instead i opted for permanent protection using ice racing screws. much happier with them. they are on all of my winter boots now.