We use US shoe sizing. When in doubt, measure your foot from the heel to the longest toe and give us that measurement in the customer comment box when you place an order. It also helps a lot if you already own a pair of Fluevogs, and let us know which style and size they are.
If you need to convert Men’s or Women’s US sizing it is helpful to know that Men’s sizing + 2 = Women’s sizing. (For example M7 = W9).
Check out our Sizing section for more details.