I'm writing this review to help with sizing. I'm a 5'6" female that wears a size 9.5 shoe and is having swelling below my knees because of pregnancy. I am satisfied with the S/M size. I was uncertain which size I needed to but. I was concerned with the fit of the small/medium even with my larger foot (for a woman) and currently swollen legs would be too tight but its not. My shoe size is 9.5, my ankle measures 11 in around, and my calf measures 16 in around. Again, I'm very satisfied with the fit of the small medium even with a larger foot and currently swollen legs. I gave four stars because I feel the socks could be slightly tighter, though I can still feel the effects of the compression. I like the height of the socks too, right below my knee but not sliding down the back of my calf.
I want to address people's comments about the toes being loose fitting. Toe area should be loose fitting in compression socks so circulation is not cut off from the toes and the socks do not squeeze the toes together causing blisters, corns, or pressure sores. This is purposeful in the design. I personally do not like tight socks squishing my toes together so I'm very satisfied with the fit of the toes, it is minimally loose. It does not create wrinkles and bunch around my toes inside my shoe which I can't stand.
Bottom line, if you're uncertain which size to purchase, get the smaller one.