Paperback formatting can be a great, big, ole ball of people getting butt-hurt over age-old rules that no-one can remember where they came from in the first place. Having said that, there certainly is a list of best practices and conventions that exist for good reason. Let's dig into how to differentiate between the stuff you can ignore, the stuff that is up to personal taste, and the stuff you most definitely should do a specific way.
This post will cover the universal sort of formatting stuff. In separate posts, we'll grapple with front matter and then sales funnels/end matter. Then in yet more posts we'll deal with specific tutorials for using Microsoft Word and Scrivener for formatting your final product.
First, let's talk about trim sizes (the size dimensions of the book). You sorta got to set this in stone before you play around with any of the rest of the formatting process. And if you plan on releasing a series or several books, you'll want to be consistent with all of this stuff, so it's worth spending some time getting it as close to perfect as you can the first time around.
There are somewhere in between twenty and a buttload different trim sizes. For trade paperback print purposes there are a few common ones that all end up being around eight to nine inches tall and five to six inches wide.
Amazon has made the nine by six inch trim size among the most popular. It is their default, and there are a couple of good reasons to just roll with it. The six by nine results in a little shorter book. The fewer pages means less expense. Less expense means you can either keep more profit or pass the saving along to your readers. If your stories are longer than 75,000 words, the larger trim size might result in a book that costs $0.25 less per copy to print.
The second convenience for the 6 by 9 trim size is the 2x3 proportions. The standard ebook cover proportions are 2x3. Stick with me through the mathematics: 2 x 3 = 6 inches wide; 3 x 3 = 9 inches tall. If that was too hard, just know that a 6 by 9 inch trim uses the same proportions as the standard ebook cover. This means that you won't have to redesign or stretch the front of your print book cover design to create your ebook cover design.
Personally, I find the only drawback to the 6 by 9 trim to be...well, personal. I just don't like it. It's too big for me, and it packs awkwardly in most box sizes. But the 2x3 proportion is significant enough that I've decided to stick with the 8.25in by 5.5in trim size (which also shares the 2x3 proportions). Be forewarned that the 8.25 by 5.5 is still not a recognized standard trim size by Amazon, so if you choose it you won't have access to Amazon's extended distribution. This is not important to me because I use IngramSpark for all distribution outside of the Amazon store. I recommend everyone do this. Using Amazon's extended distribution will get you essentially zero additional sales and will conflict with your ability to use IngramSpark, which when used correctly will provide you with significant additional sales.
The second most common trim size for trade paperbacks these days is either the 8in by 5.25in or the 8.5in by 5.5in. Both of these are similar to the 8.25in by 5.5in, but they lose the 2x3 proportions and thus seem a little ridiculous if you plan on creating several products. I'm not into adding extra steps when I don't have to.
Next we have to determine the margins. This is something that falls in the squishy category. There is room for you to exercise your personal taste in the matter. In general, don't go with less than 0.7 inch margins for the top, bottom, and inside edge (or gutter), and 0.6 inch of margin on the outside edge. I prefer 0.75 for top, bottom, and gutter while going with 0.65 on the outside edge. Some people will want more gutter, and some will insist on a 1 inch margin on top and bottom. Whatever floats your boat, but please don't go over 1 inch with your margin. That's just wasting paper.
It makes sense to tackle fonts next. Some will get contentious about this one, but there's no need to get entangled by any of the pretentious arguments about fonts. There are several that readers are accustomed to and won't result in them burning your book in angry protest. But, you must stick to one of these commonly accepted fonts! If you try to use Comic Sans or Papyrus, anywhere in or on your book, readers will burn it. Talk about contributing to global warming! You don't want that on your conscious.
If you stick with one of these fonts, you'll be fine: Garamond, Palatino, Caslon, Minion, Janson Text. I think this post is still the best when it comes to explaining book fonts: https://www.thebookdesigner.com/2012/06/picking-fonts-for-your-self-published-book/. I personally use Palatino because of the fact it has become so widely recognized and familiar. The last thing I want is for a reader to be distracted from my story by the font. All of this formatting stuff should work at a subconscious level to convince your reader that your story is familiar and appealing.
Now that you've decided on a font, you have to determine the font size. Like so many of these decisions there is an acceptable range. For a standard paperback (not a Mass Market, Middle Grade, or Large Print product) don't go smaller than 10pt and don't go larger than 11.5pt (for most fonts). I use 11pt Palatino. This is pretty big, and it will definitely result in a longer book (therefore a more costly product). The two biggest factors in influencing the length of your final product are font size and lines per page.
I have not yet added large print books to my arsenal. Once I do, I will most likely switch my standard print products to 10.5pt font in order to save pages. But for now, I stick to 11pt due to the ease of reading.
It is hard to compare font sizes by picking books off of your shelf since those books won't be considerate enough to tell you the font sizes they used, and different fonts will feel a little bigger or smaller than others. But if you have a mass market print on your shelf (one of the small paperbacks that used to be common at grocery stores or newspaper stands), it's probably printed with 10pt font. A hardback Harry Potter book is more likely to use 11pt.
Line Spacing and Page Padding
For line spacing, it is best practice to consider the number of lines per page rather than focusing so much on the actual line spacing. The number of lines you cram into each page will significantly impact the reader experience. This number can vary widely, but a good practice is to check out several paperbacks in the same genre you are formatting and see what sort of line density you enjoy.
It will quickly become apparent why we dealt with trim size, margins, and font before tackling lines per page. All of those variables impact how many lines you can comfortably fit on the page.
I personally like to land somewhere between 28 and 35 lines for a 8.25in by 5.5in trim size with 0.75in margins that uses 11pt Palatino. To hit 32-33 lines per page (my sweet spot) I use 1.2 line spacing in Word or Scrivener.
Page padding refers to the amount of space you leave at the top of the first page of each chapter. This one isn’t too particular. I’ve seen everything from four empty lines to ten empty lines. I usually roll with six empty lines, then the title, and then one empty line before the start of the body.
Headers (ie. Running Headers)
Some will insist there is only one correct way to do all of this and will attempt to eliminate anyone who strays from their formula. If you haven't gathered, I'm not one of those people. If you want to put your page numbering at the bottom of the page, you go right ahead. But here are the most common conventions.
Start your page numbering with the very first blank page of the book, but don't show the page numbering visibly until you reach the actual story. None of your front matter should display headers or page numbers, but then the first page of your story might display page 12. Blank pages and first pages of new chapters should not display a header or page number at all. You also need to make sure you are setting up your book to include "opposite pages." This means that the settings for your right-hand pages will be different than the settings for your left-hand pages.
Pages that will display on the right-hand side of your book are known as recto pages. (I've never looked this up and don't know what it means...and yes, I'm too lazy to look it up now.) Pages that show up on the left-hand side of your book are known as verso. Recto verso! [Waves wand at manuscript with hopes it will format itself magically. Shrugs when nothing happens.]
As a general rule, recto pages are supposed to display your chapter title while verso pages display your book title. I prefer to display book title on the recto pages and author name on the verso pages. I suppose if I wrote mostly nonfiction it would make more sense to include the chapter titles in the header. Pluck a dozen books off your shelf and you'll find several different versions of headers.
I do recommend you keep your page numbering either to the outside of the running header or centered at the bottom. And I definitely recommend you ensure headers don't show up above chapter titles or on blank pages. That will stand out as weird or unprofessional for some readers for sure. Recto headers should be right justified, while verso headers should be left justified so that the header is never swallowed up by the gutter of the book.
When trying to figure out which pages are recto and which are verso, here is the trick. The very first page of your formatted book MUST be a blank recto page. Right? The inside of the cover is the first thing you see on the left when you open a book. The first page is always going to be on the right (recto). And you should start your book with two blank pages, a recto page and a verso page. This means the first thing your readers will see will be your title page which will be the third page in your book and will be a recto page.
Ensure that your title page is recto by checking the margins. If your title page has a wider margin (the gutter) on the left-side of the page then it is properly set up to display on the right-hand side of your book! All verso pages will have the wider margin on the right-hand side of the page. Also double check that your running header displays properly by ensuring that the recto page header is right justified while the verso header is left justified (always on the outside of the page).
Now we've gotta sort through the weeds--stuff like headers, numbering, and indents. There is plenty of room for individual taste and expression with most of this stuff, so I'll just relate the boundaries along with what I prefer.
Let's start with the easy one--indents. Fiction uses indents, not extra space before or after paragraph breaks. Even most nonfiction uses indents. Fiction always does. The only exception is the first paragraph of new chapters. Standard practice is to NOT indent the first paragraph of each new chapter. I suppose the reasoning is that indents are for indicating the start of a new paragraph. A first paragraph is clearly a new paragraph, so an indent is redundant. I highly recommend you follow this practice. Indenting the first paragraph is pretty rare and will probably stand out as being odd.
In addition to losing the first paragraph indent, many books will either use a drop cap (fancy first letter of the first word) or fake capitals for the first 3-5 words of the chapter. This is ornamental, but it looks cool. I like to use fake caps for the first 4 words of each new chapter.
The standard indentation is around 0.35in. In the old typewriter days it was 0.5in. Personally, even 0.35in seems lavish to me. I use 0.29in as my preferred indentation. I'm not sure how I landed on that number, but I've been doing it that way for a decade and I still like it.
Full-Justified Vs. Left-Justified
You might have noticed that up to this point, I've not mentioned justification of your body text. That's mostly because I didn't want to start a fight or cause you to rage quit from the get go. You see, full-justification is a pain in the ass. When formatting a 75,000 word document full-justification will lead to hundreds of awkward word spacing issues that will require you to skim through your entire book and insert hyphens to remedy. I'm far too lazy to do this. I've gotten into chain saw battles over this one with some writers. And while a cage match is good fun every now and then, I'll just leave this decision up to you. I'm sure some readers prefer full-justified over left justified. I just don't think it is important enough to bust your butt over.
We've finally arrived at the tedious stage in the process. Yay! Now is the time to skim through your entire book and fix two main things: orphans and chapter starts. You should also keep your eyes open for anything out of the ordinary...such as bold text or writing notes that somehow slipped through. Not that I've ever published a book with notes to myself buried in the text, but you know, I've heard stories. Ehem, moving on.
Chapters should start on recto pages. This is a solid practice that should probably be upheld. We've all skimmed a book looking for a specific chapter, and if they always start on the right-hand page, it's easy to find them. This means you will often need to add a blank verso page at the end of a chapter to ensure the next chapter starts on a recto page.
Of course make sure you start this process with the first chapter and that you've done all your other editing and formatting and you've set your front matter. It's super annoying to run through this and then remember you left out the dedication...which then bumps all your pages off. Again, I assure you I've never done such a silly thing...
As you are checking chapter starts you need to also check for orphans at the same time. I think I'm using the right term for this. Anywho, you don't want there to be three lines of text, or less, on the last page of a chapter. It looks derpy. Some would say even four lines of text is too few, but I'm willing to fudge four lines.
As you can probably imagine, fixing this problem can go in one of two ways. You can either add lines or remove lines. If you've got only one extra line of text spilling over at the end of a chapter, it won't be too hard to trim the text at key points. Look for a paragraph that ends with a widow (isolated word) on an otherwise empty line. The vast majority of the time, it's not too hard to find a few throw away words such as, "just," "than," "started," "back," "before," etc. Tighten up a paragraph that results in saving a line and thus sucks that orphan line of text back onto a full page instead of leaving it isolated on an otherwise empty page.
The second option for fixing this problem is to add more paragraph breaks. If you notice a paragraph that is running for nearly half a page, that's way too long. Find a spot to break it up. Creating a new paragraph won't always result in an additional line of text. But if you break it in the right spot, it will.
Once you get good at this, you'll be able to spot places toward the end of a page where you can create a strategic paragraph break that results in the last line on that page being empty and the new paragraph starting on the next page. Sometimes doing this early in a chapter can result in a cascade effect that pushes three to four additional lines of text onto the last page in the chapter rendering two lonely lines of text into a plump, attractive five-lines.
One last warning: do this orphan line process at the same time you are fixing chapter starting pages so you don't end up undoing the work you've already done. And that's it for this post! Next we'll address front matter. That's a whole nother turd in the punch bowl of formatting.