When you fall down the rabbit hole of European and Asain stationery, your eyes are opened to a huge, wonderful world of paper sizes from around the globe.
A4, A5 and A6 paper sizes are the most commonly used in countries other than the USA. Out of these two sizes, A4 is the workplace standard with A6 being the personal standard (journals, notebooks, etc). I like A5 size notebooks, as A6 notebooks are a tad too small for me. A sizes are listed in the image below.
If you pay close attention, you can see that European and Asian paper sizes make logical sense, with sizes halving themselves from the largest to the smallest. For example, A6 is half the size of A5.
Moving on to the B size paper, these follow the same rule-of-thumb that A sizes follow, which each smaller size being half of the previous size.
B5 seems to be the most popular B size with B6 coming in second.
To my knowledge, they were the first to introduce a B6 "slim" size, which is narrower than the normal B6 size. Traveler's sizes typically do not go by their "A" or "B" paper sizes, but names such as micro, pocket, passport, and standard. You can see the sizes in the image below.
Click here for a full dossier of all paper sizes.