Order a size smaller
I wear a size 9.5-10.5 women's size shoe (my favorite shoes right now are size 9.5 MEN'S Merrills), so I ordered a Medium thinking that it would be fine since that's right between the size ranges on the chart, and I like my socks a little snug.
Nope! The socks I received are definitely the size I ordered, but they could accommodate feet at least two if not THREE sizes larger than mine. I have to deliberately leave a bit of slack in the toe and heel so make it fit correctly. Fortunately, the compression in the instep and the tightness of the band ensure the sock stays in place and "fits", but I get no actual compression from it, and they try to ride up whenever I slip on my shoes.
They're comfy enough I guess, and the thickness and color are great, but if I could do it all over again (my husband already unpacked all the socks and threw away the wrapping, so I can't return them), I'd order the Small.
ConsWay too big