Guide to Paper Sizes

The most familiar system of paper sizes is the ISO standard, which includes the common A4 sheet - these are illustrated below from A2 to A7. The ratio of all A-sized paper is 1:1.414, which means that, if you cut the sheet exactly in half, you are left with two sheets which retain the original ratio - hence if you cut an A4 sheet in half, you get two A5 sheets.