For those who needed info, here is something I compiled sometime back...
In Inches
3R - 3" X 5"
4R - 4" X 6"
5R - 5" X 7"
6R - 6" X 8"
8R - 8" X 10"
S8R - 8" X 12"
10R - 10" X 12"
S10R - 10" X 15"
A1 - 23.3" X 33.1
A3 - 11.7" x 16.5"
A4 - 8.2" X 11.7"