It depends on the brand. Check out the sizing chart. If you're not sure what your feet size is, I recommend getting it sized at a brick-and-mortar store where you find out how many inches or cm your feet length is. Then check it against the size chart listed and get the size that's the bigger of your 2 feet. When you shop Zulily, you have to know your size well in inches. I often buy different sizes based off their listed charts, and have not come across many errors. When I do, I petition hard with customer service and sometimes, they may allow an unworn item to be returned, but don't bet on it. If you have wide or narrow feet or you tend to have trouble finding comfortable shoes even when you go to a store in your local town, I would say, don't bother buying it through Zulily as you may end up being disappointed. As someone else mentioned: sometimes it's available for you to choose to buy it through the brand website instead (maybe a tad more expensive, maybe not) and typically you have the option to return.