From Sock Guy:
SockGuy’s Stretch-to-Fit sizing system means just two adult sizes, our S/M and L/XL, provide the perfect fit and performance for the majority of men and women.
All of our S/M socks will fit adult women through size 10 and men through size 9. That means most women can sport any of our S/M sock designs – ladies feel free to shop the entire site’s selection of S/M socks. Likewise, for women size 10 and up, any L/XL design will be the perfect choice to Spread the LUV all over your feet!