It is the second smallest A series paper sizes regulated by the German DIN norm. The total surface of A9 is 0,003 square meters that is - 3 cm2. The dimensions of the A9 are 37 x 52mm. While it is expressed in pixels (for the resolution of 300px) it is 437px x 614px, and in points - 104,9pt x 147,4pt.
The ratio between A9 and A0, the biggest format normalized by the ISO 216 standard is 512 to 1, which means that a singular A0 sheet of paper consists of 512 A9 ones. The said principle can be applied while calculating the basis weight of a sheet of A9 paper. One has to divide the mass of A0 (which always serves as a point of reference) by 512.