Filofax organizers come in a few standard sizes: A4, A5, Personal (and Compact, which is Personal size paper in a smaller ring size), Pocket, and Mini. There are also some discontinued sizes, such as Deskfax (which had 9 holes) and M2 (a really mini size with only 3 holes).
I recently saw a friend who loves the Deskfax size and collects vintage binders. The Deskfax paper size is actually B5, which he orders from Japanese paper suppliers.
Some people love A6 paper, which is very hard to get in North America but common among European and Japanese manufacturers. On the other hand, if you love the Franklin Covey brand and live in Europe, you have to deal with 8.5x11 paper, which is just a little shorter and wider than A4.
Are you one of those outliers? How do you get your hands on paper and organizers in sizes that aren't sold in your country?
Something to ponder as you enjoy the weekend!