Image by Bromskloss
Note that where I am (China) there is a limit on large volume printing sizes: The widest they can do is 70cm (there’s no limit on length, it’s a roll of paper). So for the largest available print size, a handy size would be:
Posters: 70cm x 99cm
This is at the A series aspect ratio, roughly 1.41:1. There’s a good calculator here. Posters are often 50cm × 70cm, almost a B2 size.
Chinese book sizes
In China they have a special system for book printing, which is based on dividing up an uncut sheet of paper that measures 88cm x 123cm. So dividing up the paper into 16 is called “16开” or “16开本”.