Ebook formatting forgives. Text reflows, readers resize, and a stray margin harms nobody. Print does not forgive: a physical book is a manufactured object with cutting tolerances, spine curvature, and a preflight check that rejects files for measurements a human eye would never notice. Almost every failed upload traces to a handful of specifications, and all of them are knowable in advance.
This is the checklist version: every number that matters, in the order the decisions have to be made.
Step 1: Choose the trim size, and choose first
Trim is the finished page size, and every other measurement in the book derives from it, so it is the one decision that cannot be revisited cheaply. For adult fiction in the US market, 6 x 9 inches is the trade paperback default: universally supported, efficient on page count, and invisible to readers precisely because it is what they expect. The compact alternatives, 5.5 x 8.5 and 5.25 x 8, suit shorter novels, where they add pages and spine presence; 5 x 8 evokes mass-market editions.
Two practical notes. Pick a size both KDP and IngramSpark support if wide distribution is possible later, and resist novelty trims: unusual sizes limit printer options and complicate any future hardcover. Genre matters less than folklore suggests; page count matters more, since the same manuscript is a thicker, pricier book at a smaller trim.
Step 2: Margins and the gutter that grows
Outer margins are aesthetic above a floor: printers commonly require at least 0.25 inches on every side, and trade fiction typically sits at 0.5 to 0.75 for comfort. The inside margin, the gutter, is structural. Pages curve into the binding, and the thicker the book, the more of the inner page the curve consumes, so gutters scale with page count: roughly 0.75 inches for books up to about 300 pages, 0.875 to around 500, and a full inch beyond. Both major printers publish exact minimum tables; meet them with room to spare, because a gutter at the legal minimum still reads cramped in the hand.
The classic failure here is finishing the layout, then adding a foreword. Page count changes, the gutter minimum steps up, and the file that passed yesterday fails today.
Step 3: Bleed, the eighth of an inch that rejects files
Trimming is mechanical, and blades land within a tolerance. Bleed exists so the tolerance never shows: any content meant to touch the page edge must extend 0.125 inches past the trim line, and the PDF page itself grows accordingly, a 6 x 9 interior becoming 6.125 x 9.25 with bleed on the three outer edges.
The decision is binary. A text-only interior whose every element sits inside the margins needs no bleed, and the file exports at exact trim. One full-page image, one chapter opener with an edge-touching graphic, one background tint, and the whole file becomes a bleed file. Mixed setups, bleed dimensions without extended content, or edge-touching content without bleed dimensions, are the single most common preflight rejection.
Step 4: The interior conventions readers expect
A professional interior follows conventions so old they read as physics. Body text in a workhorse book serif at 10.5 to 12 points, leading around 120 to 145 percent. Chapters open on a fresh page, traditionally recto, with a drop of roughly a third of the page and no running head on the opener. Running heads carry author or book title on the verso and chapter or book title on the recto, and disappear, along with folios by most conventions, on openers and blanks. Front matter paginates in roman numerals, with arabic numbering restarting at the body. First paragraphs after any break go unindented. None of this is enforced by preflight; all of it is enforced by readers, whose sense of "self-published" is mostly an accumulation of these details missed.
Step 5: Spine math and the cover handoff
Cover design cannot start until the interior is final, because the spine is arithmetic: page count multiplied by the paper stock's per-page thickness, and cream stock runs thicker than white, so the identical manuscript has different spines on different paper. To make it concrete with KDP's published factors: a 320-page paperback on white paper (0.002252 inches per page) carries a spine of about 0.72 inches, while the same book on cream (0.0025 inches per page) needs 0.80 inches, a difference large enough to misplace spine text if the cover was built for the wrong stock. Our free spine width calculator runs this exact math for any page count, paper, and trim, including your full flat cover size with bleed. Both platforms generate exact cover templates from your final specs; the discipline is simply sequence. Interior locks, page count is known, template is generated, cover is built onto it. Every chapter added after that sequence reruns it.
Step 6: Export the PDF preflight actually wants
The interior file that passes the first time has a short, strict profile: built to the print PDF standard (IngramSpark's requirements center on PDF/X-1a), every font embedded rather than referenced, images at 300 dpi effective resolution, page size exactly at trim, or trim plus bleed for bleed files, no transparency surprises, no password or security settings. Font embedding is the classic silent failure, because the file looks perfect on the machine that owns the fonts and only breaks at the printer.
A note from the trenches on that standard, and it is genuinely from the trenches: we build and maintain an IngramSpark PDF/X export pipeline inside BlurbBio, and the specifications in this article are the exact checks our own preflight passes daily, so the failure modes described here are ones we have personally hit and fixed rather than collected from forums. PDF/X conversion can be brutal to text quality if done carelessly, flattening type to images or breaking the text layer that screen readers and search rely on, so export from a tool that produces the standard natively rather than converting after the fact. This is a pipeline problem as much as a settings problem, which is why modern writing platforms with built-in print export handle trim, margins, running heads, folios, and PDF/X output as one system instead of leaving the author to assemble it in a word processor.
The pre-upload checklist
Trim chosen and supported by every target printer. Margins above platform minimums, gutter sized to final page count. Bleed decision made globally: exact trim with nothing at the edges, or trim plus 0.125 with edge content extended. Openers on fresh pages, running heads and folios suppressed where convention says. Front matter in romans, body restarting at 1. Fonts embedded, images at 300 dpi, PDF/X compliant, no security. Cover built from the final page count, on the platform's own template.
Dedicated formatting tools automate most of this list, and choosing between the two leading ones is its own decision, covered in Atticus vs Vellum. Whatever produces the file, the specifications above are what the printer checks, and books that respect the eighths of an inch sail through.
Specifications reflect KDP and IngramSpark documentation as of mid-2026; both publish current requirement tables, and checking them before upload is always worth the five minutes.
See also: Atticus vs Vellum · How to Self-Edit Your Novel · Amazon KDP AI Disclosure Rules · How to Write a Novel: The Complete Guide
