B size is much less used than A format worldwide. Indeed, it is not suitable for common use, and is not accepted by conventional photocopiers and printers. However, it is widely used by professional printers to create magazines, maps, menus.

Format B is homothetic. When a sheet is folded in the direction of its width, we get the smaller size, and it is from the larger format size folded in 2 that is obtained X format. So we can say that B(x) = 2 x B(x-1) = ½ B(x +1). Thus, the proportions are always preserved, and we can easily reproduce a page and its contents to a higher or lower B size.

Sizes A, B and C are all based on the √2 ratio. This implies that the length of every B size sheet must always be equal to its width x √2 (or 1.4142). We thus obtain the following formula: a / b = 2 b / a = √2.

These formats, and in particular the B one, come from Lichtenberg Professor of Physics, who in 1786 praised the merits of √2 ratio in a letter to his friend Beckmann, itself written on a sheet applying this ratio. This proposal was echoed by Walter Portsmann, who proposed it to the DIN (Deutsches Institut für Normung, German Institute of Standards) in 1922. It was necessary to harmonize german formats.

It accepted it and standardized it for Germany. To its success, even beyond the borders of countries (42 countries had already adopted this standard), it was taken by the ISO 216 1975 for international use.

While the format A was created on the basis of a surface (A0 measures strictly 1 m²), format B was based on a measure of size: B0 width is1 meter.

As such, it is easy to know the width of all B formats dividing B0’s one. However, it is more complicated to calculate its weight, since the weight of the paper is most often expressed in g/m², in reference to A0.

B format is widely used by professional printers worldwide, except in North America, where other formats are used (Letter for example).