Review on Tilos 3Mm Waterproof Neoprene Fin Socks - Ideal For Scuba Diving, Snorkeling, Swimming, Watersports, Hiking & More! by Devon Dober

Fit perfectly and the large fit my feet (10 1/2) and my son's (11 1/2) just fine. Now my feet are slightly wider than my son's.We wore these for scuba fins in tropical waters of the Florida Keys. Just make sure you don't wear them all day wet or your feet will shrivel up. I would always take them off after a dive and rinse them or they'll start to get rank. Also, no hard bottom so you'll feel everything under your feet (still better than barefoot).