I'm normally a size 6.5 in women's --- also sometimes a 6, sometimes a 7, depending on brand --- and the Size 6 flats were entirely too small. I wound up returning for a Size 7 and they fit perfectly! These are incredibly comfortable with a cushioned heel.  Living in Florida, they tend to get hot and make my feet sweat but nothing some super low profile socks/liners couldn't fix. These have become my day-to-day shoes!