I believe a small is 5/6 a medium is 7/8 and large is 9/10, bought a pair of these for my daughter-in-law in large she wears a 10 and they fit her just fine, so I'm assuming medium is a 7/8.
Don't miss out, very soft and comfortable wearing and the color is vibrant pink and green, excellent for the beach or pool and look great with denim or khaki...excellent quality footwear.