I wear a size 7 shoe. I prefer my sandal socks to be somewhat loose, but the mediums (for shoe size 8 -9 1/2, I believe) I ordered are uncomfortably snug, hard to get on, bunch up and wrinkle around the ankles causing major dents in the skin and discomfort. I have a couple pair of fleece sandal socks from SolSox. I prefer roomie socks and those were roomy and yet secure
Soft Grey / M (W 8-9 M 7-8)