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Do you sometimes wonder what those A or ISO marks mean on that stack of clear bond paper that you’re buying at the office supplies shop?

Paper sizes vary depending on the printing or design needs of an individual. They are also categorized, interestingly, based on conventions from different countries. For example, in North America and Europe, paper is categorized by loose sizes (e.g. letter, legal, tabloid) ISO (International Standard) and ANSI (American National Standards Institute). In the United Kingdom, paper is measured based on what’s called the imperial system, which are also used by some shops in the US. will discuss only the sizes of paper that are most commonly used by institutions today.

1. ISO 216

ISO 216 is the widely adopted paper standard convention worldwide. Most sources note that this series of paper sizes was inspired by the idea of Georg Christoph Lichtenberg on aspect ratio. Lichtenberg noted over three centuries ago that when paper is folded in half, both sides should measure equally. ISO 216 includes the A and B series, although there are also C series paper under a different ISO superset (ISO 269). One defining characteristic of this convention is that each sizes is half the size of the size before it (e.g. A5 is half of A4, etc).


The American National Standards Institute is also a popularly used paper convention globally. Also known as loose sizes, it has set de facto sizes for its series which include ANSI A (letter), ANSI B (ledger tabloid) and so forth. ANSI sizes have a corresponding equivalent in ISO sizes, although they don’t measure exactly the same. Like ISO standards though, ANSI sizes have the same aspect ratio when folded in half.

3. Imperial or British sizes

Imperial or British sizes are determined by the number of times the paper can be folded as well as the type of sheet used. For example, royal paper when folded thrice will produce eight leaves to sheet. Also considered as loose sizes, imperial standard paper sizes are quite arbitrary and may sometimes be one or two sizes smaller than the size before them.

To determine which size of paper is great for your book or document, please refer to the tables below:

Interested to know more? You can read our articles on the history of paper, different types of paper, and how paper is made in our Journal.

Explore our various paper products today:

         Lazer IT Copy Paper                                         Pressboard Folder                                             Acura Stick Notes