Birkenstock holds the strong belief that their sandals and shoes enhance people's quality of life, and add to their health and vitality. Plus... they're just so darn cute! Birkenstocks are an orthopedic shoe designed to fit end to end with no extra room. They only come in whole sizes and are usually adjustable across the top of the foot to hold your foot into place.  
It depends on how your foot fills out the shoe but we generally suggest:
Womens 5-5.5 = 35
Womens 6-6.5 = 36
Womens 7-7.5 = 37
Womens  8-8.5 = 38
Womens 9-9.5 = 39
Womens 10-10.5= 40
Womens 11-11.5= 41
Womens 12-12.5= 42