4A0

While 4A0 could hypothetically refer to a sheet with dimensions four times that of A0, this much larger size has not been officially added to the ISO standard. The A series formats are based on the aspect ratio of √2 and designed to scale by factors of √2 rather than multiplying. There are no intermediate sizes between the existing A numbers (such as A0 and A1).

The origins of the A series date back to late 18th century Germany, when scientist Georg Christoph Lichtenberg proposed the √2 aspect ratio in a 1786 letter. This geometric ratio was adopted for the German standard in 1922, which later informed ISO 216 published in 1975. However, the ISO standard has never extended beyond A0 as the largest size.

So in summary, 4A0 is not an actual ISO standard paper size. The A0 dimensions of 841 mm x 1189 mm remain the largest in the A series according to ISO 216. Larger sizes like 4A0 may exist informally but they are not recognized or defined in the official international standard at this time. The ISO 216 standard only specifies the paper sizes from A0 to A10 in the A series.