Birkenstock sizing

[HellonHeels]

Any views on Birkenstock fit? Are they true to size?

I'm a 5 and wear a 4 - the 5s were ridiculously big on me.

I'm a 4 and have to wear 3's I bought a pair of 4's and they were ridiculously big for me. I have red patent and a white and cherry print pair but I wear my red ones daily.