I wasn't sure what to expect on sizing, I wear a 10.5 - 11 in most shoes, I ordered the 11-12 to be on the safe side. I believe a 10-11 would be just fine, but it doesn't matter. It's like a sleeping bag for your feet and as long as they aren't too small they're fine. With the draw string you can easily adjust these so they won't fall off. I don't feel the need to take them off when I put my feet up on an ottoman. The rubber lettering on the bottom is sufficient to prevent slipping. The only down side at all is no footbed / soul so there's no support at all. So you wouldn't want to go for a walk but they're great around the house. As house slippers I'm happy with them and would recommend them as such.