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It blows our hivemind that the United States doesn't use the ISO 216 paper size standard (A4, A5 and the gang).
Like, we consider ourselves worldly people and are aware of America's little idiosyncrasies like mass incarceration, the widespread availability of assault weapons and not being able to transfer money via your banking app, but come on - look how absolutely great it is to be European:
The American mind cannot comprehend this diagram
[Diagram of paper sizes as listed below]
ISO 216 A series papers formats
AO
A1
A3
A5
A7
A6
Et.
A4
Instead, Americans prostrate themselves to bizarrely-named paper types of seemingly random size: Letter, Legal, Tabloid (Ledger) and all other types of sordid nonsense. We're not even going to include a picture because this is a family-friendly finance blog.
Commercial printers will print most everything on A0 paper, but since all metric paper is doubling or halving sizes with respect to each other, they can tile a bunch of print jobs into the same A0 paper and then cut them apart, saving machine time by turning a bunch of small jobs into one big job.
US printers also do this, just using larger ANSI sizes instead of larger A sizes. Or they just use rolls.
But US paper sizes don't tile nearly as well as metric paper sizes do, is the point
They do tile, they just don't share an aspect ratio. Two letter sheets make a tabloid or ledger sheet (depending on grain direction of the paper), and two tabloid sheets fit on a broadsheet, which generally comes in rolls so there's a bit of trim because the size comes from actually physically dealing with paper, which is why they're also the names of the newspapers that were printed on them. Like, it doesn't go down from letter like ISO a sizes do, but it generally works well enough.