Paper Sizes - a quick reference!

The most common system of paper sizes in Europe is the ISO standard All sizes are given in millimetres

The aspect ratio of ISO paper sheets is 1 to 1.414 (the square root of 2). This creates a useful property; if you cut an A sheet in half the resulting parts will be the same proportion as the original. This also creates two sheets of the next A size down, for example an A4 cut in half = two sheets of A5.

You may hear about two other paper sizes, the RA and SRA, which are used in print manufacturing. These are larger than the A sizes to allow for trim marks and bleed. Some print jobs will also require to go on B sizes if they are non standard.

(The ISO system is much rarer in the USA)
Please bookmark this post to keep as a handy guide!