Common European Print Size Equivalents

hello all:

i'm working on a project and would like to know what are the most common size prints used in europe for photo albums and frames. here in the US, we commonly use 4x6, 5x7, and 8x10 as well as 2x3 for wallet-sized photos.

what are the equivalents used in europe? metric measurements are, of course, fine!

thanks,
scott