I wear a size 7.5 or 8 in women's shoes and I ordered the size 6 in men and it fit like a true roomy size 8 in womens. There's plenty of room for thick socks in the winter or thin socks with room for your toes to breathe in the summer months. I've worn these daily all winter and they are waterproof and keep your feet warm with or without thick socks. I'm ordering more in different colors!