The medium size cap that I ordered is PERFECT! It fits perfectly over a silicone cap that I also wear. I wear these every day when I swim in the morning at 6 am. The small size that I bought 1.5 years ago was not my correct size, but that was my fault. I love this cap. I have been making my first purchase work by adding my own velcro strip that I stapled to the strap because the velcro eventually wears out. Still, I will buy another when my recent purchase wears out. Thank you!