The A series is considered to be the most popular paper size in the world (the majority of countries use it as a standard one). It also has to be pointed out that the most recognizable A series paper size is the A4 one.
The series in question is predominantly based on maintaining desired proportions.
Each and every sheet of paper is created by means of making a fold running along one of the edges (see: scheme below). Georg Christoph Lichtenberg is considered to be the creator of the aforementioned series. At the end of 18th century, he was the first one to discuss it in detail in his publication. He was also a person being responsible for the standardization of all the formats taken advantage of in Germany, as he introduced the so-called DIN norm, the name of which was later on changed into ISO 2016. After some time, it was adopted by a significant number of countries all over the world. The said norm defines A, B and C paper size series.
Each of the A series formats is based on the number specifying the dimensions of paper. In the case of each and every of the sizes, the shape is always a rectangle, the shorter-to-longer side ratio of which is always 1 to √2. Interestingly, the original A0 size has exactly 1 square meter of total surface. It has to be also pointed out at this point that the smallest paper size available is called A10.