The most common international paper size is the A series. You probably remember from your school days having to buy A4 pads to go in your folders and A5 notebooks for jotting things down. While the dreaded homework diaries where typically A6 so they could easily fit in your pocket.
The most commonly uses paper size is A4 with most printers and documents bring printed on A4 paper.
An A0 size piece of paper or card is defined as having an area of 1m2. This makes sense within the metric system. The rest of the paper sizes in the A-series (i.e. A1, A2, A3… all the way to A8) are half the area of the previous one. In other words, A1 has covers have the area of A0, A2 has half the area of A1 and so on.
This is achieved simply by halving the larger length of the previous size. For example, A0 is 841 mm by 1189 mm and A1 is 594 mm (half of 1189) by 841 mm (same as the width of A0).
This is exceptionally useful as you can make an A4 size brochure by folding an A3 piece of paper in half or an A5 leaflet by folding a piece of paper A4 paper in half. This clever sizing system allows scaling from one size to another (as provided by photocopiers and computers) without compromising the aspect ratio (the number that you multiply the shorter side by to get the length of the longer size).
The aspect ratio for A-sizes is the Ö2 which is around 1.4142. This allows A-sizes to be scaled one to another without compromising this ratio. In other words, things don’t look stretched or squashed when you scale up or down from one size to another.
The advantages of basing a paper size upon an aspect ratio of 1:2 were first noted in 1786 by the German scientist and philosopher Georg Christoph Lichtenberg. But enough about the science how about the sizes and uses:
A0 size is 841 mm by 1189mm or 33.1 inches by 46.8 inches. This is commonly used for very large posters and displays that you see on big exhibition stands.
A1 is 841mm by 594 mm or 33.1 inches by 23.4 inches. You’ll be familiar with A1 as it is the size of flip chart pads as well as large posters favoured by University students.
A2 is 594 mm by 420 mm or 23.4 inches by 16.5 inches. This is used for medium sized posters.
A3 is 420 mm by 297 mm or 16.5 inches by 11.7 inches. This is used for noticeboard posters or for drawing large diagrams. It is frequently used in printing to produce A4 size brochures or leaflets by printing on both sides and then folding it in half.
A4 is 297 mm by 210mm and is the most commonly used size. Home and office printers print on A4 and most documents and letters are printed on A4 size. It is also a common size for loose-leaf notepaper for students and business people. Many printers print on A4 to fold this in half to create an A5 leaflet.
A5 is 210 mm by 148 mm or 8.3 inches by 5.8 inches. It is a common size for small note pads, diaries and flyers.
A6 is 148 mm by 105 mm or 5.8 inches by 4.1 inches. This is the size of most postcards and small diaries or reporter’s note pads.