Very good question to ask! I remember tying to find this information and it was such a pain to get hold of!
So I'll try to go over the facts that I know!
Firstly, a big part of it turns out to be less about the comics format and more about your region. Different countries have their own ideas about what size a book should be, and the printers they work with have certain preferred sizes.
Since all printers print on larger paper and crop the pages down, there's actually a fair bit of flexibility, which is why even the prose books at your local bookshop can vary wildly in size.
Most book publishers outside of comics aren't that bothered about size so long as if the size is something weird and outrageous there's a good reason for it. A book that's about as wide as A4 but a bit shorter in height isn't significantly harder or more expensive to print than A4, and just requires the machinery to be set for that print run, so for the kind of size of runs done on a book for a commercial publisher (thousands of copies), this isn't a big deal. Where a publisher might go "UH....no." is if you decide "I'm printing a long scroll format webtoon, so my pages are really tall and narrow" and print something that requires the cost of A3 size pages to print and bind to fit your comic's sheer height on, while also being really wasteful due to how narrow the pages are. What you'll get is a very expensive novelty book that's also a pain for book shops to put on shelves so they might not stock it!
For self-publishing, looking at what printers will do in your area is generally best. Most printers these days use digital printing for short runs of a hundred or so books like you'd expect a webcomic with a modest following to sell, and that means that yes, so long as your pages are at a nice high resolution, you're pretty much good to go. If you can be a clean unit like "double the print size" or 1.5 times the print size, I've heard that the quality is better but... the difference may only really be discernable if you're looking for it very closely.
The one time where I will say size and resolution 100% matter and you need to pay attention is: SCREENTONES! If you have drawn a manga-style pure black and white comic with dot tones, and you do not print at a size that's exactly full, half or maybe 1.5x size, you run the risk of "moire" on your tones; them turning into strange chequered, lined or tartan-like patterns. Take care, manga peeps!
In the UK, if you're self-publishing, an easy approach is to go with our standard paper sizes: A4 or A5 being most common. We don't have specialist comics printers here, so you're generally printing with companies that mostly print brochures and the like. (Mixam is a popular choice that comes well-recommended). Most of the comics I've made have been A5 for this reason, and the one time I made a Japanese Tankobon sized book was because the comic was originally a Tokyopop Rising Stars of Manga entry. It still cost the same as if it was A5 and the binding and cover lamination were a little iffy, so perhaps going very small for what a printer is used to is where problems can happen.
In the US, there are businesses that specialise in comics where I think they do expect files at "comics size" If printers or publishers have preferred sizes, they will typically provide you with a template. You can often find these on their websites in an FAQ, resources or submissions section. US comics size is a fairly safe choice, and plenty of templates exist for it online. If you're submitting to Marvel or similar, ALWAYS draw at US comics size!
Finally, the best thing you can do to "future-proof" your comic if you're undecided is to follow these rules:
- Always draw your pages at minimum 300dpi and keep these high res "raw" files safe, then save copies you scaled down to web size for upload.
- Always work so that there's a big bleed on full-bleed panels and keep all important stuff like speech bubbles and enclosed panel borders a full centimetre in from the inner edge of the bleed. This way if you need to resize pages to a slightly different ratio, you'll have a lot more space to play with.
