A4 Paper

The whole ISO series of paper, and, for that matter, most things in Europe, is based on the metric system (a cool thing we should use (save for measuring Guinness (always measured in pints)) but don't). A4, the paper that most closely maps to US letter sized paper, is 29.7 cm tall by 21 cm wide, or 11.7 by 8.3 inches.

In contrast, US letter is 11 by 8.5. As you can see on the picture on the right, this makes A4 (the white piece of paper in the back) a bit narrower but a bit taller than US letter (which is the yellow page).

If it is only a slightly different size, you may be asking why bother? A pretty fair question. It is the height-to-width ratio is one of the things that makes it so cool.


The ratio of 21:29.7 (width to height) is the same as 1:1.4142, also known as 1:(square root of two). The fact that this is a defined ratio is quite appealing to me intellectually.

In contrast, there is no clear objective basis for "8.5 by 11" or "8.5 by 14." Basically, they were how big many paper makers were making sheets of paper at the time the US government made the standard.

What's more, going from one size to another is a function of doubling or halving a sheet (depending on the application). A5 is 14.8 cm wide by 21 cm tall--a piece of A4 cut in half. A3 is two pieces of A4 side-by-side. (42x29.7cm).

That is pretty nifty in its own right. However, it is particularly cool when trying to work a copier. Reductions are done at a fairly constant ratio. Going from A4 to A5 is a reduction to 71%. A5 to A6 is...71%. This looks like it would make going from size to size quite easy.

Again, the US system doesn't allow for such a clear progression of size. As the sizes do not completely relate to one another, scaling from "legal" to "letter" means there is white space.

Unfortunately, aside from my own personal notepads and the odd UK-based magazine, I don't get to work with A4 that much. It is still a cool thing.