3R? 4R? Help with sizes!

As an american transplanted to Hong Kong, I am having problems knowing what size to print my photos at. We just used 3.5" x 5" and 5" x 7" and such in the US, but here it is 3R, 4R, etc... Can someone help me and give the measurements in inches or centimeters for what these photo sizes are? I've looked on the internet and haven't found a site that lists them. I have found that 3R is 3.5" x 5", but that's about it. Thanks a bunch!!!

Google always smiles at me.

http://www.gammaphoto.​com/svct_color_automat​ed.html

I used "paper sizes 3r 4r 5r". If you add mm and/or inches to the mix you'll probably find better sites.

Hey, thanks! Yeah, google's always been good to me as well, but I just couldn't seem to get the right search phrase in this case. Thanks!

For anyone else looking at this post to find the sizes, here's what I've found:
2R = 2 1/2 x 3 1/2
3R = 3 1/2 x 5
4R = 4 x 6
5R = 5 x 7
6R = 6 x 8
8R = 8 x 10

thanks having it post (joking_15)

any other sizes? please le t me know'' Im new in this thing