I wear the same size - a Euro 40 - in Birkenstock and Dansko.
The only one that differs for me is Alegria, where I wear a 39.
You really have to look on the manufacturer's official website's size charts, and then take into account what your unique feet and toes are like.
Since my 2nd and 3rd (LOL) toes are both a lot longer than my "big toe", I have to leave room for 'em by going up a half or full size in any footwear.
(except, again, for the Alegrias, where their sizing for a 39 is 9 to 9.5)
HTH 