B series papers are used as an alternative where the A series is not suitable. Similar to the A series papers, its dimensions are defined by the ISO 216 International Standard for paper sizes. Using B series is a good idea when the A series is too big or small for the document you’re working on.
The sizes offered by the B series are between each of the A series paper sizes. B5, for instance, measures between A4 and A5.
Following the same concept as the A series, a sheet of paper in the B series, when folded in half, will result to the next smaller size. B3 is half of B2, B2 is half of B1, and so on. Like the A series, the B series’ aspect ratio is 1:√2.
While less frequently used in office settings, the B series is relevant for a variety of special uses. Most posters use B series papers and B5 is a common choice for books. Other uses include envelopes and passports.