📄 rule

Aside from the 1 to √2 ratio, the area of A0 paper is exactly 1m². People behind ISO 216 thought of everyting.

Which is awesome, because every number up halves the size. This, combined with the standard way that paper weights are given (e g. 80g/m2) allows you to easily calculate how much a piece of paper weights: 1 A4 80g/m2 weighs 5g (1/2^4 * 80g)
- Now it makes even more sense!
People behind ISO 216 thought of everyting
how to make a good standard:
step 1: copy from DIN
https://en.wikipedia.org/wiki/ISO_216#History
- Well, Germans are pretty anal about standards (thankfully) and they do them right, so why not copy them?
From their website: "We're ISO, the International Organization for Standardization. We develop and publish International Standards."
- Sadly, ISO in recent decade started to do bullshit. They don't pay for standard development, they don't employ anyone for standard development, they collect membership fees from national standards organizations, require payment to download most standards and don't allow to copy published standards. Also they retroactively paywalled a lot of standards.

Wait, the US genuinely doesn't use A4 etc.?

We have trouble fitting all our freedom on your kooky, internationally-recognized sizes
Here’s a comparison using the most sensible units possible:
- Ngl as a Canadian, I implicitly thought 8.5x11 was A4. Well that's dumb, we should switch.
- Also, I'm pretty sure A4 runs through an American printer just fine.
Letter paper (8.5" x 11" | 215.9mm x 279.4mm) is kinda sorta pretty close to A4 (8.27" x 11.69" | 210mm x 297mm) so without having the two next to each other, it can seem like A4 is just a funny piece of letter, and vice versa. But to answer the actual question, USA and Canada (and apparently the phillipines???) use the "North American Standard" which is a terrifying mess in comparison to the beauty that is the ISO standard.
Edit: typos
- Philippines makes sense, being a former US colony
- Tbf, I can see the use case for some "non-standard" sizes, like Legal, where having more height to the page without the extra width might be useful for readability of long documents.
  ...can't think of an excuse for the rest, though.
- I think Mexico too, or at least the paper name is "carta" and "oficio" which would translate to letter and legal (kinda)
Do you have a moment to talk about 8.5 x 11?
- Make it quick there's an important call coming in about my auto warranty
Their hole puncher has three holes and binders/folders have 3 rings as well
- How many have yours got? More or fewer?
  I have seen legal/letter sized clipboard with two rings, for the short end of the paper.
No, we mostly use Letter, Legal, etc. When you use photoshop to print, you would pick letter or legal usually.
https://goodcalculators.com/paper-size-conversion-calculator/
- 11x17 is incredibly common too. Usually it is oriented landscape and z folded to get a large diagram into a document. It's kind of irritating that the most typical large format size is 24x36, which is a different aspect ratio than 11x17, for a variety of reasons. If you're designing something you need to know what aspect ratio to design for. Most copiers can do 11x17, and if the standard large format size was 22x34 it would be exceedingly easy for most offices to produce good working copies of large documents. Best compromise I've seen is when people put a logo or header on the side that can be omitted when you switch aspect ratios.

Wait a second if the bank app can't transfer money how do they do it? Just barter with guns? Are the bullets like coins?

We involve third parties to help spy on our transactions.
It’s OK, they charge us for the privilege.
- Wtf?
  Also are banks just dumb or what? Has it crossed their greedy minds that they also can charge to make transfers?
We have a fee-free bank-to-bank transfer system that is based on pre-digital technology that takes 2-3 business days. We often call it "direct deposit" or automated clearing house (ACH). It's often used for payroll and paying bills.
Now, we could probably make this payment system instantaneous relatively effortlessly (and thus useful for regular in-store purchases), but the banks lobby against this so they can continue to charge us fees and interest to over-use credit cards. (Interestingly enough, credit and debit cards all use direct deposit on the backend to actual transfer funds between parties).
This is all fine and dandy for most people because they simply can't imagine doing things a more consumer-friendly way.
- Your comment is all true, except - we CAN all imagine it, but as you pointed out, our unchecked hyper capitalism prevents it
- We have a fee-free bank-to-bank transfer system that is based on pre-digital technology that takes 2-3 business days. We often call it "direct deposit" or automated clearing house (ACH).
  Ah, right, kinda like SEPA Credit Transfer. You do need a persons IBAN which is a bit long, but their name is validated so you usually send it to the right person.
  Now, we could probably make this payment system instantaneous relatively effortlessly
  Ooh, cool, kinda like SEPA Instant Credit Transfer, which transfers money within ten seconds to bank accounts using the above mentioned number.
  This is all fine and dandy for most people because they simply can't imagine doing things a more consumer-friendly way
  And that's why, in the Netherlands, Tikkie took the country by storm. It is an app that allows you to use iDEAL (a web-based payment system, soon rolled out in Germany and Belgium as Vero) to send money to friends. Usually takes one pin and three taps to send it, and have it instantly appear on the account of the recipient.
- I imagine it has also something to do with safety? Like, if it was instantaneous, that means you can do damage instantaneously, or a hacker might have fewer hurdles to go through.
Venmo, Zelle, Cash app, etc.
My last 3 banks all had ACH transfers in-app, too, so idk what they're smoking
- And the ACH only takes three business days!
- ACH transfer to a friend’s bank account?
- Like most things, it depends on which state you're in.
i just assumed people used 3rd party services for ease of use or faster transactions, seems so wild that you'd not be able to send money using your bank to me
here it takes 1-2 business day for a free wire transfer from one bank account to another, and you can do it in your banking app or on the bank's website. you just need to authenticate with your online pin code. you can also pay 1€ to get a <24h transfer
it's honestly much better than using a third party service, since pretty much everyone has a bank account, and pays using a card tied to that account directly
- Brasil enters the chat
  No fees transfer takes seconds, as long as it's not international. People use it for buying groceries, clothes or paying for whatever they buy in the middle of the street from other people who are not businesses. Confirmation of payment from receivers end is immediate with a push on your phone.
  All sellers can produce a QR code including receiver address and price to be payed. All bank apps scan and pay seamlessly.
- In Canada we have Interact e-Transfer. Basically all the banks colluded to make a system that allows for instant money transfer between banks using email or phone number as the recipient identifier, along with options for comments and security questions.
  I felt like this was a huge step up compared to all the hoops and third party apps I had to use in Europe.
- Idk what all this talk is about - we have wire transfers in the US. I don't need a third party to do it either, it's exactly as you've described, I can do one through the bank's app or on their website, and it's free. It's not as common though since the information required is: Name of the recipient's account exactly as it is, account #, routing #, and exact name of the bank tied to the routing #. You can save that info though to make it easier to transfer the next time around - it's very useful for close family and friends.
  EDIT: Turns out I have two different ways of transferring money. One is just moving money between accounts, can be at the same or a different financial institution, has the same functionality as a wire transfer, is free, and doesn't rely on third party apps. A wire transfer is apparently done via some federal system and does require paying $20 or so, but I haven't had to do a wire transfer in forever. I'm not sure why anyone would want to do a wire transfer.
SEPA is not to take for granted.
- Isn't sepa the eu system?
  Sorry but bank transfers are not 1st world exclusive, it's common place in 3rd world as well.
Actually, a lot of banking apps can be used to transfer money now, it's just done through Zelle. We can also do a bank transfer using the routing and account number (at least with my banking app) but that I think takes longer.
They can. Idk about the availability for all banks but we have something called Zelle.

fun fact: the length to width ratio of ISO 216, √2:1, is the same ratio as the tritone in an equal tempered 12-tone musical scale. If you fold A4 paper in half, you get a piece of paper with the same length to width ratio as before; analogously, if you invert a tritone, you get another tritone.

As famously read from letter-sized sheets:
I know it should be a fun fact but I can’t quite grasp it.
But is it a diminished fifth or augmented fourth?
- Ackchyually...
That is fun!

idk why the image says "european", the standard is worldwide. only north america and parts of latin america don't use it afaik.

Japan also has their own system.
- Japanese use JIS but A size is the same with ISO so there's no confusion here. For B size there's slight difference in JIS and ISO, but as end user I hardly print anything other than A4 so haven't encountered problems myself.
I know Brazil uses the A# format, dunno about other latin countries.
- A Sharp?

The annoying "letter" paper size is for some unknown reason what windows always sets as the paper size unless I change it to A4 manually. Naturally if I forget the printer won't print. US paper sizing - annoying me on the other side of the Atlantic.

File I'm printing: A4 PDF
Default printer setting in Windows: A4
Default setting on printer itself: A4
Setting that gets chosen automatically in the print dialog: Letter

Is this why my printer has wierd size "letter", that is not sized like letter?

Yeah, US software always defaults to their own non-compliant standards instead of looking at the location and determining the default that way.
That is why we in Europe and all the other parts of the world get these strange fuzzy prints where the text is almost unreadable, and is cut off on strange parts in the text.
- This sounds like our bad, sorry.

My country (not USA) uses American paper. I hate it.

Do Euro printers say PC LOAD A4?

I think they probably do.

I want to only briefly defend the NA system in terms of naming. I get it, I worked in printing for decades, I know how shitty it all can be. But Letter and Tabloid communicate well for something that is otherwise all the fault of press guys.

Well, it's 2024, so they mostly say things like "out of A4 paper - load A4 paper in tray number 3". But yeah, they used to.
- Interesting, no photos of that message come up.
Well, one still could do it like how many countries transitioned to the metric system: slap the traditional names onto things that are actually now defined by the metric system, like how China's catty, about 0.60478... kg, became 0.5kg. Just slap "Letter" onto A4.
- That’s going to make some driver developers very upset. And sensors in printer cartridges that can sense both A4 and Letter.
  I say we just balls the whole thing. Screen or pencils.
yes, thats why i always was confused when i heared people online talk about pc load letter.
i kinda assumed it was just an odd way to refer to paper that some manufacturers used
You really think people are too dumb to remember 2 letter codes that are literally printed on everything? Come on man :D

It's a beautiful standard that works wonderfully until you have to deal with any actual measurements. 210 x 297 mm - so easy to remember and divide.

Letter is 215.9mm x 279.4mm lmao
- Good thing Americans don't use metric, that sure would be an awkward size.
- No it's 8.5 by 11.
  See? Easy. Also you really have to try to get your hands on something that's a different size. 99 percent of printer paper is Letter.
- Excuse me, I believe you meant to say:
  215 ⁵⁷/₆₄mm x 279 ³⁸/₉₆ mm
i mean, i've never needed to divide the size of a standard sheet of paper - if i need a smaller variant, i can just fold it in half and cut it. when working with paper, it's pretty easy to do physical math, and you rarerly need something that's perfect down to the millimetre
regarding the size- it's just something you learn through life. school supplies lists typically specify the size of notebooks and paper you need to buy in centimetres, so year over year, you quickly learn that A4 is 22:29.7, and the slightly bigger standard notebooks are 24:32
- so year over year, you quickly learn that A4 is 22:29.7, and the slightly bigger standard notebooks are 24:32
  Pretty sure you just justified Americans using Fahrenheit ;)
I don’t disagree! And in the interest of fairness I feel compelled to include an obligatory xkcd:
https://xkcd.com/2937/
300-3 isn't that hard to remember. also i don't know why you would need to divide it. they're both divisible by 3 if that helps.

As a math nerd, I appreciate the fractaline nature of your paper.

But as an american, what is the practical advantage?? The sizes are so far apart, and you dont get papers with different ratios? Like for example Letter and Legal are both 8.5 inches wide, can be used in any standard cheap household printer, legal is just longer so you can fit more stuff on the page. Letter paper folds into thirds to fit snuggly in an envelope and legal folds into fourths. Other paper sizes are so niche and rarely used why does it matter if theyre a perfect mathematical ratio or not?

The advantage is folding.
When folded at the middle it becomes the next size.
So if you have an A4 paper but don't have the proper C4 envelope, you can fold the paper in half and put it in a C5 envelope. This is standard.
Let's then imagine that you don't have a C5 envelope either, but only have the remaining Christmas card envelopes, which are C6. So you just fold your paper one more time at the middle and it'll fit again.
Also, the area of A0 is 1 square meter. You probably don't nornally have an A0 paper around, but that doesn't matter, because you can take 8 pieces of A3 or 16 pieces of A4 papers, tape them together and it'll be A0.
Now it isn't actually a square meter. It's the same area, but it's not square. No, the length and width makes the golden fucking ratio. This might be irrelevant for a legal document, but it's pretty neat if you want to make a nice drawing.
Paper come in reams. Reams come in boxes. Boxes come on pallets. The paper boxes fit perfectly on a pallet in both length and width, so the layers of boxes can be placed either way in an interlocked pattern. This is mostly a box design thing though. American paper also fit on American pallets, but without the connection through the sizes, you cannot make a pallet with mixed sizes and expect it to fit.
Forgot to add: the real beauty isn't the paper size. It's simply having a standard. Cans and bottles and lots of stuff follow similar metric standards. It's possible to mix everything and still make it fit snuggly on a euro pallet.
- Isn't the ratio of length and width of A-papers square root of 2 and not the golden ratio?
- But that's not something i have ever actually needed.
Scalability. You can design something in A3/A4 and if you want the page in a smaller, common format, you can print it as A4/A5. This is especially handy for designing flyers, or scaling bigger stuff (like schematics, which are usually drawn on A1/A2) down to print it on household printers.
It's also quite convenient that pretty much anyone has a common understading of what A3/A4/A5/A6 is, when talking about areas in real life.
Also, if you need A5 put only have A4 paper, you can cut it or even split it without scissors. That usually even gets better results, because splitting a piece of paper in two by folding is easier to do precisely that to do it whith scissors.
Making a page longer just to "fit more stuff on it" isnwt really such a great boon, since you always need a cut-off somewhere.
A4 can be folded into thirds as well and smaller envelopes are perfect for A6.
- yeah, this is a great thing!
  i usually make class notes recap on A4 pages, and can then print 2 A5-sized pages side by side on a single standard A4 paper, no need to rework the formatting. messing with the printer options, you can pretty easily get it to do a small booklet off of your standard A4 word document, just need to staple it together!
- It's also quite convenient that pretty much anyone has a common understading of what A3/A4/A5/A6 is, when talking about areas in real life.
  We know “the size of a sheet of printer paper” and also that size when “folded hot dog” or “folded hamburger”.
  Y'all can’t fold ‘em fish ‘n’ chips, ever heard any food terms used to refer to length/wide folding?
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.
Just use multiple pages if needed?
Who needs all their words on a single huge page like some sort of scroll?
- It takes less paper to print 1 page of legal if that's what your text fits on than it does 2 pages of normal paper if said text doesn't take up all of the second piece of paper.
  When you're printing large documents (10 or more pages let's say) that starts to be significant savings in thickness of a stack, too.
  It's not one huge page, it's an extra 2 inches, or ~25% longer

Wait... You can't transfer money with a banking App???

Not really sure about that one, I've been able to transfer money with my banks app for more than a decade. Not all US banks are created equal.
- Not all US banks are created equal
  I think that's the issue. Also how common direct deposit for paycheques in the US? I hear it's rare but in Canada, it's the norm and all our banks here can do e-transfers.
I've been able to transfer money through my banking app for a while without issue. Not sure where that came from in the post, cause it's not true lol.
Yes. I can transfer money to someone just by knowing their phone number. I can do it on a Sunday afternoon and they get the money instantly. I haven't used cash for more than a decade now. Haven't used a card for at least 5 years.
Zelle is a thing with my banking app.
My sister has a credit union bank account and her app has it. I have PNC.

America got someone triggered over paper.

Shooting ourselves in the face to own the mets

Let's not even start with the metric system (used everywhere) and the imperial system (used in the usa and some african countries).

Don't let the UK get away with their bs as well, they use a mix of metric and imperial. Imo that even worse bc at least america is consistent with their bs measuring system
- Most annoying is cars. We buy fuel in litres but measure our cars efficiency in miles per gallon, meaning I either have to calculate how many gallons I put in my car or how many kilometres I've driven to work out if I'm being more or less economical.
- And Canada. I hate that map of the US and Burma. The US uses metric as it is part of customary units anyway. I also wish metric was base 12 or 16.
- Americans aren't consistent either. 2 liter and similar bottles (and it's not even the same bottle, like they aren't reusing molds or anything, it's just an American 2 liter bottle). Sharp edges and points like on mechanical pencils are in millimeters. So are many nuts and bolts. Stuff like electricity and power are measured in metric units. Generally electronics/computer parts are in metric, the main exception that comes to mind is screen size, which even the rest of the world does in inches (LIKE WTF!?!).
  There's plenty of examples of metric units in the daily life of an American.
According to wikipedia: "Some imperial measurements remain in limited use in Malaysia, the Philippines, Sri Lanka and South Africa." - so, not even "some", just one African country, and limited use.
- Uh, I've never used inches, nor know anyone who does - a South African
- I should've looked it up 🙈 I heard it once and didn't have the countries in mind anymore.
The best part is the US Military and NASA both use metric. I love that fact.
- Except for the UI.
  During the Apollo program they had very limited computer capacity in the capsule and lander. Computers were huge machines back then and they had to fit one in a spaceship.
  The Apollo computers used metric internally for all calculations. Anything shown to the astronauts however was in imperial, as metric was apparently too complicated for astronauts to comprehend. They had to waste precious computer capacity converting to imperial because even astronauts can’t handle anything else.

The US also doesn't officially use the metric system sigh.

The US officially uses the metric system...to define the US customary system of measurements.
E.g. 1 foot is defined as 0.3048 meters.
- That was just ONE aspect of the adoption of the metric system. And that was done to make backwards compatibility easier because of long lasting legacy systems. Because some systems, like say plumbing in a home or city, last for a very long time before they get replaced or repaired. New plumbing installations often use Tubing like PEX which is metric. I designed and fabricated a dozen brackets for a US customer over the weekend for delivery today. They were made using millimeters as specified.
  And if you actually pay attention to how the metric systems compares to the US customary, you would see just how closely they are related from the start. Which makes sense since what we call Imperial measurements predate the metric system by several hundred years.
Yes, yes we DO use the metric system officially. In the early 1970's the metric system was made the official standard for weights and measures.
What we didn't do was force everyone to use it at 3:11AM 11/21/1974. It was decided to take a longer approach and let the change happen naturally and it has happened.
Everything in the grocery store is marked with metric weights and volumes. We buy butter by the gram, soda pop by the liter and whisk(e)y buy the milliliter. And everyone is looking for that same missing 10mm socket/wrench. (Where does do those things go anyway?)
How much more metric do we really need to adopt?
- Well, milk is still sold by the gallon, butter is still divided into tablespoons, nutrition facts are still defaulted to cups and ounces. Wood is still sold by the foot or yard, cars still measure speed in miles per gallon, people still know their height and weight in feet and inches and pounds.
  Could be worse but could be a lot better, too.
- The 10s are being held hostage by the 12.5/48.78 wrenches
- There must be some invisible 10mm black hole just vacuuming up all the 10mm sockets and wrenches in the world. I can’t even tell you how many damn 10mm sockets and wrenches I’ve bought and I still only have one of each. Probably none. I haven’t needed to wrench anything in a couple weeks.

PC LOAD LETTER? the fuck does that mean!?

It means there is a tiny scrap of paper lodged in one of the uptake wheels in the paper tray.

Lol, people find the silliest things to be angry and indignant about.

Found the American.
- There are easier ways to find us! (get a map, ask strangers to point at anywhere but North America; the first incorrect answer or anger response will probably be one of us)
- What an idiotic thing to say in a comment to a post not written by an American, that's complaining about Americans.
I guess someone never used ISO 216.

I am just grateful paper isn’t measured in hands

What the fuck, that was way more hilarious than a blog post about financial securities messaging ought to have been

Relevant CGP Grey

Damn, you beat me to it.
Here is an alternative Piped link(s):
Relevant CGP Grey
Piped is a privacy-respecting open-source alternative frontend to YouTube.
I'm open-source; check me out at GitHub.

1.414, the magic number.

Not-super-fun fact: an 8.5 x 11 inch paper can be useful if you lack a ruler in an American office & you need to measure an inch or a foot.

If you fold the paper like in an image I'll try to attach, the hypotenuse is 12.01 inches.

Edit: then you fold the 12.01 inch side against the 11 inch side to get a 1.01 inch measurement

Not exact, but good enough if you need to know your neck size to buy a fancy shirt online - not that I would ever waste my corporation’s time that way!

Not-super-fun fact: you can measure in metric with school notebook paper.
Each sqare is 0.5 by 0.5 cm.
EDIT: 0.5 cm, not mm. For measuring 0.5mm I can use 0.5 mm mechanical pencil lead.
Also there is coordinate paper:
0.1 by 0.1 cm. Or 1 mm grid.
- I love how that OP’s solution requires an inexact technique to achieve an even less exact measurement. Like Americans really out here being proud of the stupidest shit
- Tiny nitpick: I think you meant 0.5 by 0.5 cm (or 5 by 5 mm).
- I use it a lot if i need to draw something that is x long. If you do a lot of graphs for example you can use the measurements on your ruler.
Not exact
The motto of the whole imperial unit system.
And most people here know that an A4 is 21 (exactly) by 30 (roughly) cm, which you can use (surprisingly) use for measurement aswell.
- 21x29.7
  This number is permanently stored in my memory, just like 1€ = 6.55957F
How does that work? 8.5^{2 + 11}2 is 193.25, square root of that is 13.9. Where does 12.01 come from?
- Huh. . That’s weird. I could swear I double checked my math before I posted this One Dumb Trick online years and years ago…
  Found the mistake, I had skipped a step, updated original post
Oh no, it's getting worse!
Oh, that's simple and useful.
What a nightmare

What NA does not do this what the fuck, backwards ass country in so many ways.

Right but this is definitely the most prominent & important reason
- Much like how England colonised everyone and still hates spices, America also bombed and invaded everywhere but still hates decent measuring systems.

dude devastated americans xD

To be fair, A4 yields unwieldy pages that are too long to comfortably read. And when do you ever need the feature to fold an A4 sheet into A5?

I use the "A5 booklet" function all the time.
I do this all the time. I print two pages on one A4 sheet (or rather four, two on each side) and then fold them so they are like a leaflet.
That's the main advantage of the system – you don't have to design things differently depending on how big you want to print them. You can scale the same design to an A6 flyer or an A2 Poster.
And when do you ever need the feature to fold an A4 sheet into A5?
When you want to read it more comfortably for example.
Are you american? If so, the "unwieldy and too long" is probably because you're not used to it. I'm not used to letter-size and it seems weirdly short and unnecessarily wide but I know it's because I'm just not used to it.
- I’m German. If the pages are a comfortable size, why does no publisher ever use A5 or A4 paper? To quote an answer I gave to another comment here:
  Let’s check. I grabbed four random German books from my bookshelf. If you’re right, the pages should either be roughly 30cm×21cm (A4) or ~~15cm×10.5cm~~ [Edit: 21cm × 15cm] (A5).
  Book 1: 18cm × 11.5; book 2: 19cm×12.5cm; book 3: 20.5cm × 12.5cm; book 4: 24cm × 17cm. None of those conform to the standard.
  Another hint that the paper format is weird is that scientific papers on A4 are always either printed in two columns or use the ninths rule for margins, i.e. 1/9 of margin on the inner and upper edges and 2/9 of margin on the outer and bottom edges, essentially throwing away almost half of the page (I’ll admit there are more economic recommendations of 1/11 or 1/13). This is to make the columns narrower to get closer to the target of 60–80 characters per line. Note also that this makes the ‘usable’ area approximately 20cm long, which is much closer to the American’s ‘Legal’ format (216mm).
A4 is 17.6mm longer than an 8.5x11" sheet of paper.
And when do you ever need the feature to fold an A4 sheet into A5?
https://www.youtube.com/watch?v=pUF5esTscZI
- I'm sold, we should botch all other formats for origami
- Here is an alternative Piped link(s):
  https://www.piped.video/watch?v=pUF5esTscZI
  Piped is a privacy-respecting open-source alternative frontend to YouTube.
  I'm open-source; check me out at GitHub.
almost all consumer printers are for a4.
i had (rare) occasions where i wanted to print a picture for an a3 sized frame and was able to glue together two a4 prints.
also, as far as im aware, books in a4 size actually consist of a3 sheets bound together in the middle. (same with other sized books)
- almost all consumer printers are for a4.
  I never said A4 wasn’t the standard. I said it’s not a good one.
  books in a4 size actually consist of a3 sheets bound together in the middle. (same with other sized books)
  Let’s check. I grabbed four random German books from my bookshelf. If you’re right, the pages should either be roughly 30cm×21cm (A4) or ~~15cm×10.5cm~~ [Edit: 21cm × 15cm] (A5).
  Book 1: 18cm × 11.5; book 2: 19cm×12.5cm; book 3: 20.5cm × 12.5cm; book 4: 24cm × 17cm. None of those conform to the standard.
Where I'm from, it's super common to print A4 in half size and fold them into a little booklet when you need to distribute a few pages to loads of people
Lmao, it does not.
Skill issue

I dunno, it doesn’t look so good once you get to “Etc.” size.

Especially those A20 cheat sheets are so damn hard to read
- i hate it when they only give out A20 exam sheets

TIL that there are different standards of paper sizes in other parts of the world. I never encountered this before despite living in Germany for 10 years, probably because the last time I was there was 30 years ago.

do they go down to A -1, A -2 and so on

Not officially, but unofficially there's 2A0, 4A0 and so on. Bigger than that is rarely used however.
Even smaller?!
Edit: wait they’d be bigger
No just A0, A1, etc. A5 being for cards, A4 being the average used in schoolbooks and such, with A3 mainly used for posters, never seen anything larger in everyday life.
- Ad posters on the street are usually A2 to A0

Eh, letter's height to width ratio looks better.