Purchased these for our 18 year old son to wear around campus. While he wears an 11.5 in running shoes we chose an 11 in the Under Armour slides. He wears them daily and reports that they are quite comfortable.
These Under Armour flip flops are built like iron, and only twenty bucks. I would buy again tho, on my feet, the top hurt the top of my feet - rubbed, too tight - until I broke them in. I wear a women's 10 WW and the MEN'S size 10 fit perfectly.