Avoiding Standard Paper Sizes — Pie Books
There is some real math behind the rectangular sheets of paper. At least if you work with ISO paper sizes. Measurements of the widespread A4 are derived from the size of A0 – it has an area of exactly 1 m2. For the B series every next size is also half as large (or twice as large – depending on the direction you choose to go) as the previous. B0 is defined by the length of its larger side – it is exactly 1 meter long. Both of them have the same aspect ratio: square root of 2.