B5 paper is a standard size within the B series paper sizes defined by ISO 216. It measures 176mm x 250mm, making it a bit smaller than A5 paper. The aspect ratio of B5 paper is also 1:root2, just like all other B series paper sizes.
B5 paper is commonly used for printing books, catalogs, and other materials where a compact size is desired. It’s often used for printing travel guides, pocket-sized books, and similar materials. It’s also popular in Japan, where it’s commonly used for printing manga and other comics.
The B5 paper size is larger than B6 and smaller than B4. It’s also smaller than A4 paper, which is the most commonly used paper size in many countries. When compared to A5 paper, B5 paper is slightly wider but shorter in length. B5 paper is also slightly smaller than the popular US half letter paper size.
Just like other paper sizes in the B series, B5 paper size has a useful property for enlarging and reducing documents. Enlarging from B5 to B4 size, or reducing from B5 to B6 size, results in the same aspect ratio, making it easy to scale up or down while maintaining the same proportions.