Havaianas Women's Top Sandal Flip Flop, Ruby Red, 35 BR/6... In most shoes I wear a size 10, sometimes a 10.5. I used my judgement, with the help of some of the reviews and went for the larger size (41/42 or US 11/12). They fit perfectly and are comfortable. If you're somewhat between sizes and sometimes lean toward the larger size, I would say definitely get the larger size in these flippies!