Sizing depends on the brand and type of water shoe. Closed-toe shoes often require a size larger, especially if you are using them for hiking or water sports; however, this rule of thumb is not universally true. To get the best fit, try shoes on in the store. If you do buy online, read the reviews and manufacturer's instructions to see whether the shoe runs true to size, large or small. Also, consider whether you will wear the shoes in winter when you might also need to wear thick neoprene socks. In that case, you might want to order a size larger than you typically wear.