this post was submitted on 30 Aug 2026
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Oh, let's also remember that A4 is a member of beautiful variant of an "SI system for paper". Want a paper the size of an A4 folded double? We have A~~8~~5. Want something that folds perfectly to A4? A3. One more fold? A2.
Edit: Did a fat-fingering
A4 folded is A5
Yes, I did a typy-type with chubby morning fingers
A85?! That's gotta be minuscule!
with A4's divide-by-two shtick an A85 might unironically have a surface area of only like a couple atoms. it's too late in the night for me to calculate this so i pass this task onto someone else
So, A0 has an area of 1 m^2^ and it's halved for each next one in the series, giving A85 a surface area of 1/(2^85^) m^2^ = 2.585×10^-26^ m^2^ = 0.02585 pm^2^.
The smallest atom is the hydrogen atom with a Van der Waals radius of 120 pm which gives it a surface area of 4×π×120^2^ pm^2^ = 180956 pm^2^ or just over 7 million times larger than the A85.
Funnily enough, a deviation of +- 1.5mm is allowed according to the ISO standard, so it is technically allowed to be much larger than that.
What on earth are you on about with those numbers? 😅
A0 is the base size, with an area of one square meter. Fold that in half and you get A1. Fold that in half and you get A2, and so on. Regular printer paper is A4. You’ll rarely, if ever, see sizes smaller than A6.
I fat-fingered the A5, otherwise the numbers were right?
I'm aware how the system works, I just wrote about it using A4 as the "base". A3 is what you fold to get A4, A2 folds to give A3, etc.
I didn't know A0 was exactly 1m^2^ though, TIL!
This made it sound like you meant that folding an A3 sheet twice gives A2 😅 Might just be my reading comprehension, though!
Nah, your reading comprehension is just fine, I just worded myself in a pretty verbal way. I totally get how it could be misread, I was thinking along the "salesman making a pitch" line:
"Want something that folds perfectly to A4? A3. Want an extra fold before you get there? We have A2!"
I have a pocket notebook size A7. A6 is too big for some pockets.
The print shop I worked at did everything at size C1, but they were a blueprint shop
Cs are the envelope sizes.
That's really weird.
c1 is approx. 3 feet long by 2 feet other long. we did lots of stuff you could roll out or hang on the wall.
I was hoping that there was a metric baseline for this paper size, but it still bugs me that the dimensions aren't "even". 297mm? That's no better than 8 1/2 inches.
There is, but A4 isn't the baseline, A0 is.
A0 is 1m² with a ratio of 1:√2. Cut that in half along the larger side and you have A1, half it again and you have A2, etc. on down the line.
The entire series maintains the same exact ratio down to A13 at 9mmx13mm.
So ridiculously dedicated to metric that they didn't think to make A0 an exponent of 2, and then designed an entire system around dividing it by 2.
A0 should've been 1.024 meters.
You’d still get «weird» lengths in the other dimension, though. Remember, the aspect ratio has to be 1 to the root of 2 for the folding in half to work.
Also, I don’t think 1024 would have been such an obvious number back in the late 1700’s, when this system was first thought up 😅
There is a system of sizes where the shortest side of the base size is exactly 1 meter, though: the B system. The aspect ratio is the same as for the A sizes.
1 is an even power of two. 1 = 2^0^
I see what you’re saying, but the «weird» dimensions are what makes the whole thing with folding in half to get the next size work:
The aspect ratio has to be 1 to the root of 2 for it to work, and that’s going to make some dimensions «uneven». The utility of that system is worth it many times over!
It's based on the 1m² A0, fold it in half to get A1 and so on.
The proportions stays the same too
There is also B4, which is 353 x 250 mm. Not perfect, but you can more easily see how they got 250, as B0 is 1414 x 1000 mm.
And IIRC A0 is 1 m².
Beautiful.
really really close to, but not quite.
They do have a paper that can fold once to get a US letter though; i am only posting about it because i only learned about it two years ago: 11x17, aka, "tabloid" size.
Some desktop printers can even print on it.
"Letter" size is standardized as ANSI A, "Tabloid" as ANSI B, and something that could be folded twice to get letter would be ANSI C. https://en.wikipedia.org/wiki/Paper_size#Standardized_American_paper_sizes
These paper sizes are used in engineering.
And that's how you choose a system over another,because it makes things easier
does all this A paper standerd business have to do with the fact that you can't fold any paper in half more than 8 times?
https://youtu.be/65Qzc3_NtGs
I feel like to really bust the myth they should have then unfolded it to make sure it was still intact.
No, and Mythbusters proved that you can.
There is 11"×17", it's called Ledger paper.
This doesn't make the american system okay.
? Ledger paper has to do with the green lines, not the size
Oh, sick! I think you mean paper designed for accounting, i.e., ledgers, while Grey is referring to the US standard size of the same name almost certainly named for that purpose.
Bingo bango.
american sizes do the same thing, just only five steps in ANSI sizes, and not really that well known outside of the industries that use the paper sizes, such as printing shops.
smallest being u.s. letter (A4 equivalent) is "ANSI A", 8.5x11in...
largest being the full sheet (A0 equivalent) is "ANSI E", 34x44in...
with the expected three steps between for B, C, and D.
going smaller than u.s. letter and ANSI A.. letter halved (4.25x5.5in) 'half letter' is a common notepad and post card size; and halved again (2.12x2.75in) is a common label size.
The aspect ratio of the A series of paper is √2, so every doubling or halving of the size retains the same aspect ratio. If you want to save paper and print at half size, you can just do that and it works flawlessly. However doing it this way means very unmemorable decimal unit dimensions.
Half letter and tabloid are much taller than letter so you have to either have overly large margins on the top and bottom, or you have to reformat your document if you ever want to change the sizes.
Though specialty paper suppliers do sell 22x17 paper if you really want to double fold to get letter paper. 11x17 is twice the width of letter which works for printing bifold books in letter size. Its just the scaling aspect ratio thing. Sizes in multiples for bookmaking do exist in both systems.
https://www.youtube.com/watch?v=pUF5esTscZI
What's the next step up after A0?
2A0, and next 4A0, but there are rarely used. From A0 you mostly print from rolls, so you define the width. Large offset printing presses use formats that allow multiple A sized pages, either single or double for binding, and the needed trims.j
I'm going to open the world's first 256A0 print shop
A series paper billboards would be interesting to see.