## A1 size is the second largest A size standardized by ISO 216. The only larger A size standardized is A0. There are larger sizes: 2A0, 4A0, but these are not ISO standardized.

The proportions are always conserved between A formats, regardless of their size. Indeed, the Lichtenberg ratio, which was taken over by Walter Portsmann and DIN (Deutsches Institut für Normung, German norms Institute), and which gave birth to the international standard ISO 216 is always respected: 1.4142 (a / b = 2b / a = √ 2) Thus, the A1 size is two times larger than the A2 size, but also two times smaller than A0. This means that a A1 sheet is obtained by folding an A0 in its length.

The proportions are always conserved between A formats, so that the content of the page is always adapted if you want to enlarge or reduce its size.

The surface of the A1 size is 50 cm ² (or 0,6 square yards, 5.38 square foot, 775 square inches). It is most often used by architects, engineers or industrial designers. It is rarely used for a classic professional or family purpose.

A1 format measures 841 x 594 mm or 33,11 x 23,39 inches. Its length corresponds to the width of the A0, and its width corresponds to the length of the A2. Its printing surface is 791 x 554 millimeters when the conventional printing margins are applied.

A1 format is ⅛ of 4A0, ¼ of 2A0, ½ of A0 for larger sizes, and 2 A2 sheets, 4 A3 sheets, 8 A4 sheets... for smaller sizes.

One can easily calculate the weight basing on the A0 (measuring 1m ²) as the weight of the paper is always expressed in g/m². For example, for a paper of 100g/m², we say that a A1 sheet (measuring 0.5 m), weighs 100/2 = 50 grams.