Here is a size chart for Birkenstock Shoes (Women's) for US to European sizing

US Size                 European Size

4 1/2 to 5                      35  

5 1/2 to 6                      36    

6 1/2 to 7                      37      

7 1/2 to 8                      38     

8 1/2 to 9                      39     

9 1/2 to 10                    40    

10 1/2 to 11                  41  

11 1/2 to 12                  42  

The narrow filled footprint will fit US AA to B Narrow to medium width feet

The regular open footprint will fit US B - C Medium to Wide width feet

 Thanks for reading my guide and hope this is helpful!