The international A series is very easy to use. The ratio of the sides is always the square root of 2, i.e. divide the length by width and it will ALWAYS equal 1.414. This also means that when a piece of A-sized paper is cut in half along the longest side, the new smaller sheet will have an area that is half the original, and with the ratio of the sides being still the same. This means that, for example, you can stick two pieces of A4 paper together along the longest side and it becomes one sheet of A3, or vice versa, cut an A3 sheet into two A4 sheets.
To calculate the area of any A-series sheet, use this simple formula:
area (in square metres) = 1 / (2^n)
where n = value of paper size, e.g. for A4 paper, n = 4
thus area = 1 divided by ( 2 raised to the power 4 ) = 1 / (2 � 2 � 2 � 2) = 1/16
so an A4 sheet has an area of one sixteenth of one square metre.
Look at A0, put in the 0 and the formula is: area = 1 / (2^0) = 1/1 = 1
A0 has an area of one square metre.
The sizes increase in number by 1 as they halve in area, thus the series goes A0, A1, A2, A3, A4, A5, A6, etc.
The A series of paper is mathematically perfect as well as being very useful in offices around the world where it is used, because of its ability to retain its shape when halved or doubled in area. US paper sizes cannot do this, as the ratio of sides is not 1.414.
