Birkinstocks are great, good quality sandles, but the sizing is odd. I bought them for a gift for my husband. I know his American shoe size (11) and even measured other shoes of his to make sure I was getting the right suggested size. The manufacturer even says if you're between sizes to go up. I ended up getting him a 44 and they were way too big. We went to a brick and mortar store and it turns out he needs a 42, which translates to about an American size 9.5  I was able to exchange them at the store and didn't go through Amazon's returns.

The shoes took a couple days for him to break in but now he says they are the most comfortable sandles he's ever had. They are highly recommended as long as you know what size you need. I took off one star for the sizing issue.