## A9 size is the second smallest size of A formats. It was designed by Walter Portsmann in 1922. He suggested it to the DIN : German Institute proclaiming all standards. Walter Portsmann then took over Lichtenberg’s proposition of 1786.

The latter then boasted the interest of proportional √2 ratio between the length and width of the sheet. DIN 476 was then taken abroad in 1975 under the name ISO 216.

A9 size is not a format that can be written. This is reserved for professional printing to create coupons or tickets. Its surface is 0.0019 m² (or 0.02 square foot, 3.1 square inches). Therefore we can put 512 A9 sheets into a single A0 one.

The dimensions of an A9 sheet are: 52 x 37 mm or 2.05 x 1,46 inches. This is a small size format.

The proportion of length/width ratio is always kept between two A format sheets, since the ratio √2 still applies. This means that the length must be equal to its width x √2 (ie 1.4142). Thus, the content of the pages never changes when you want to transform it through printing for example.

It is possible to calculate the weight of an A9 sheet based on that of an A0 sheet. As we know that A0 is measuring 1 m², we know that for paper of 160 g/m², an A0 sheet weighs 160 grams. However, the format A9 is 512 times smaller. We can therefore say that A9 weighs: 160/512 = 0.31 grams.