What is the size of calendar 9?

Regarding the question of whether 9-opening paper is b4 or b5, let me answer: 9-opening paper is neither b4 nor b5, because b4 is the normal opening paper of 16 and b5 is the normal opening paper of 32. Here, it is necessary for us to learn and understand the knowledge about paper. B4 and b5 are two specifications in China's national standards, and b4 and b5 are signs of integration with international paper standards. People all over the world know that it is the China standard.