This was a result of the normalization ratio imagined by Lichtenberg in 1786 in a letter in which he explained its practicality, the letter itself was written on a √ 2 ratio sheet.
Since then, the proportions between the different A sizes are always respected: 1.4142 (a / b = 2b / a = √ 2). This allows you to convert smaller or larger, a sheet of paper without changing its content.
A2 size measure twice the A3. Its surface is 0.25 m² (or 0.3 square yards, 2.69 square foot, 387.5 square inches). Its width is equal to the length of A3 and its length is equal to A1 width. Its available printing surface, including recommended margins, is 544 x 380 millimeters, while its total area is 594 x 420 mm or 23.39 x 16.54 inches.
A2 format is widely used for posters or calendars. This is a format that requires a very expensive printer, which is why most A2 are still printed by professionals.
The A2 size is equivalent to ¼ of A0 or ½ of A1 (larger sizes) or 2 A3 sheets, 4 A4 sheets ... (smaller sizes).
To calculate the weight, it must refer to A0, measuring 1 m², as paper weights are indicated in g/m². Thus, it takes 4 A2 pages to form an A0 one, therefore, for a 120 g/m²paper, a A2 sheet weighs 120/4 = 30 grams.
It can for a poster, a blueprint, calendar...
Buy a printer A2 is very expensive, this is why the majority of impressions are made by printers.
If you printing a valuable document like a poster, it's clearly better to ask a laminating paper. It will protect your work from scratches, dust and all other damages.
Don't forget : A2 paper printing are mostly print on a single side.