Comment by dsr_ a day ago
Nearly everything in the US uses letter, legal (letter but longer), or tabloid (double width letter, to be folded over).
Much to my surprise, a random check of a US-based office supply company shows that they do have A4 in stock -- at a price about 40% higher than letter-sized.
I used to work at Kodak and they had an industrial printer division in my building. They would go through pallet-fulls of A4 for their testing. Only place Ive seen it in use in a business setting in the US.
> Legal size folders exist and are widely used by people who use ... legal size paper.
Sure. But I didn't know I use legal size paper or even what it is before I asked the apartment complex to print the lease agreement, and it didn't fit in their own folder with the other move in papers. In my rank of weirdness discovered upon moving to the US, this is at about the same level as the different ounces.
I'm just about old enough to remember (in the UK) foolscap paper, an imperial size also a bit longer than A4. You never see it any more (at least I don't) but foolscap sized box-files are still readily available. I guess a slightly bigger box than you need is not usually a problem.
Don't forget my favorite size, "statement". This is half of letter size. Sometimes used for small statements, sometimes used as letter folded.
Hacker News users may be familiar with Julia Evans (http://jvns.ca) who creates technology zines that work in both A4 and Letter sizes, folded in half.