I actually bought these for my mom but had to ship back as they were too small for her (and me also).  She wears a 9 1/2 - 10 shoe so thought these would be ok, but hoping not to have to return them I tried them on, I wear a 9 - 9/12, but I think these run small so needed the X-large instead.  For me they were just a inky bit too short and I felt that my foot overlapped the walking surface a bit.  For my mom they were way short but the width of her foot fit just fine.  She likes this style as they keep her ankles warm.  They made my ankles feel claustrophobic.  The Amazon store they were bought from gave great customer service upon return and would highly recommend them.  So bottom line is take your mom with you when you buy her slippers!