How the sample boundary is calculated
Amazon has never published the algorithm behind sample delivery, but the pattern is consistent enough to plan against. A Kindle eBook preview delivers roughly ten percent of the total file — and the important word there is file, not story. Your title page, copyright notice, table of contents, dedication and epigraph are all inside that ten percent. A print book using Look Inside behaves differently: Amazon serves approximately ten physical pages, which at ordinary trade formatting works out near 2,750 words regardless of how long the book is.
That difference matters more than most authors expect. A 90,000-word novel gets a 9,000-word Kindle sample and a 2,750-word print preview. The same opening chapter can comfortably clear the bar in one format and be truncated mid-scene in the other.
The tool subtracts your front matter from the sample budget, places the boundary, and compares it against two positions you supply: the inciting incident, and the point where the central conflict becomes legible. It is arithmetic, not judgement. The same inputs always return the same verdict, so you can re-run it after each revision.
Kindle versus print: two budgets, not one
Treat Kindle and print as separate distribution problems, because Amazon does. The Kindle budget scales with your manuscript: word count times ten percent, rounded to the nearest word, then front matter deducted to leave story words a browser actually sees. A 45,000-word novella grants a 4,500-word Kindle window; a 130,000-word epic grants 13,000. Print never scales. Whether your manuscript is 50,000 or 150,000 words, Look Inside grants about ten pages. At 275 words per page for a typical 6×9 trade paperback with 11-point type and single leading, that is 2,750 words minus whatever front matter was rendered as images or text in the preview. Check both numbers every time. An author who optimizes only the Kindle budget ships a paperback whose preview ends before Chapter 1 finds its rhythm. An author who writes a tight 2,500-word opening for print leaves Kindle browsers with thousands of unread sample words that could have carried another beat. The tool lets you toggle the format and see both boundaries without re-entering the manuscript data.
What counts as front matter and why it matters
Front matter is anything before your first line of story. Count it exactly as Amazon counts it: the HTML or EPUB file from the first byte, not from where you think the story begins. Title page, copyright page, also-by, dedication, epigraph, table of contents, map, and any foreword or note-to-reader that appears before Chapter 1 are all inside the ten percent. A typical self-published novel carries 400 to 800 words of front matter. A nonfiction proposal with a long contents page plus an author note can easily carry 1,200 to 1,800 words. One memoir reviewed for this guide carried 2,100 words before Chapter 1 — nearly a quarter of its 9,000-word Kindle sample contained no story at all.
Audit your file. Open the EPUB or the DOCX that you upload to KDP and count, in a single pass, every word from the first line of the title through the last word before Chapter 1 begins. Do not estimate. Do not ask your editor for a guess. The sample arithmetic amplifies small errors: 500 excess words of front matter is 500 words of story that your browser never reached, and for a print preview that represents nearly twenty percent of the entire window.
If you use Kindle Create, the app injects its own front matter handling, but Amazon still measures the delivered file. If you upload a hand-built EPUB, the inclusion of a linked contents page costs you whatever words it contains. There is no special case where Amazon skips the front.
Defining the two beats the tool measures
The tool needs two word positions that describe whether a browser understands the book.
The inciting incident is the moment the protagonist's normal life ends and a new problem begins. In a thriller it is often the discovery of a body or a threat. In a romance it is the first collision between the two leads that cannot be ignored. In a business book it is the claim that reframes the reader's current approach as broken. Ask which scene, if cut, would make the rest of the book impossible. That scene contains the incident. Note its approximate start word. Precision to within 200 words is enough — the arithmetic is not sensitive to smaller shifts.
The central conflict is the moment a browser can answer, in one sentence, what the book is about. A reader should be able to say she is reading about a detective who must find a missing girl before a snowstorm seals the town, or about a founder who must fix churn before her Series A collapses. That clarity rarely arrives in the same scene as the inciting incident. It often comes 2,000 to 4,000 words later, when the protagonist commits to a goal or the antagonist's plan becomes legible. For nonfiction, central conflict is the promise the book will keep: the system it will teach or the transformation it will deliver. Record its start word as well. If your opening delivers both beats back to back in a single scene, record them as close together; the tool will report both as visible and you will see the margin for each independently.
If you write short fiction collections, anthologies, or multi-POV epics where the first story or first POV is not the hook, note the word position of the first point where a reader unfamiliar with the book would know which story this is. The tool does not care about labels, only positions.
Reading the verdict and its margins
Pass means the incident lands at least a thousand words before the boundary. A browser reaches the turn, reads the immediate reaction, and has room to feel its consequences before Amazon asks for money. A pass that also clears the central conflict by several hundred words is stronger still, because the reader not only saw the turn but understood what the book is about. Nothing structural needs to change for a clean pass, though front matter hygiene is still worth checking.
Warning covers two different problems that deserve different responses. The first is the thin pass: the incident clears the boundary by only a few hundred words. The reader sees the turn but the sample ends before it lands. On a 7,500-word Kindle sample, an incident at word 7,200 with front matter at 400 is a warning even though it is technically visible. The fix is usually 300 to 800 words of space — less front matter, a tighter opening, or a slightly earlier incident. The second is the near-miss: the boundary falls just short of the incident, often by less than 2,000 words. The sample reads as competent and uneventful, which is a harder objection to overcome than a sample that is obviously not for you. A near-miss at 8,200 words with an incident at 9,100 is more dangerous than a fail where the incident sits at 15,000, because the latter at least signals to the browser that she has not yet reached the book. An incident that sits far outside the sample can still be addressed, but it is not confused with a book that has no story.
Fail means the browser finishes the preview without ever learning what the book is about. The sample ends at word 7,500 and the incident sits at 11,000. The prose can be excellent and the verdict will still be fail, because the ordering problem is invisible to the person sampling. Reviews will say the opening was slow. Ads will bounce. The failure mode is not craft but placement.
What actually moves the boundary in priority order
There are only three levers, and they are not equally cheap. Work them in this order unless you already know the manuscript needs more than a trim.
First, trim front matter. Anything consuming more than about fifteen percent of the sample is worth attacking before any line of story is touched. A dedication and a copyright page are enough for most fiction. A full table of contents in a novel rarely earns its place in the preview — readers navigating by Look Inside are not jumping chapters. A small-caps author note or a three-page excerpt from your last book is exactly the kind of material Amazon will show a new reader before she has read a word of the new one. Cutting 600 to 1,000 words of front matter costs nothing in craft and immediately shifts the boundary outward by the same number of words.
Second, move the incident earlier. This is the most effective and the most expensive, because it is a structural edit. Cutting or compressing the opening setup by 1,500 to 3,000 words often improves the book independently of Amazon. The strongest rewrites do not cheat the incident earlier with a flash-forward that then rewinds. They compress backstory and routine until the turn arrives naturally within the preview window. If your incident currently lives at word 10,000 on a 75,000-word novel, moving it to word 5,500 is a revision that most beta readers would call an improvement even without knowing the sample exists.
Third, manage chapter cadence. If Chapter 1 runs past the boundary, the sample ends mid-chapter with no cadence. Splitting it so a chapter break lands just inside the sample gives the preview a deliberate ending, which reads as craft rather than truncation. An early break at word 4,500 followed by a short Chapter 2 that carries the incident to its consequence can make the sample feel complete even when it is not. This is the subtlest lever and the one most authors overlook, because they judge chapter length by estimate while Amazon judges it by word count.
Front matter targets by format
For a Kindle sample, aim for front matter under ten percent of the sample budget and ideally under 600 words flat. On a 75,000-word eBook with a 7,500-word Kindle window, that is at most 750 words and preferably less. On a 90,000-word book, it is 900 words at the ten percent mark, but the absolute target still matters: a 1,400-word opening preamble on a book of any length wastes preview real estate that could have shown story.
For print, aim for front matter under 15 percent of 2,750 words — about 400 words. Above 600 words you show less than 2,100 words of story and the sample becomes more copyright page than hook. Avoid filler pages that exist only to bulk the print file; Amazon still counts them.
Worked examples with the arithmetic shown
Note: the following examples are hypothetical and illustrative rather than sourced case studies.
Take an 82,000-word thriller with 1,400 words of front matter. The Kindle sample is 8,200 words, of which 6,800 are story. If the inciting incident sits at word 7,900 measured from the start of the file, it clears the boundary by 900 story words — a warning, not a pass, because the reader meets the turn on the last page of the preview and never sees a consequence. Cutting the front matter to 400 words moves the boundary to 7,800 story words and buys 1,000 words of runway without touching a line of the novel. That single edit converts a warning into a pass and leaves the paperback preview still short, which is a separate conversation.
Consider a 95,000-word romance launched in both formats. Kindle gives 9,500 words; print gives 2,750. Front matter is 700 words. Story in the Kindle sample is 8,800 words; story in print is 2,050 words. The inciting meet-cute sits at word 3,800 and the commitment to the relationship — the central conflict — arrives at word 6,900. On Kindle, both beats are visible: the meet-cute with 5,000 words to spare, the commitment with 1,900 words to spare — a pass on both beats. On print, only the meet-cute survives; the central conflict at 6,900 is cut off. The print preview in this configuration sells the characters but not the promise. The fix that addresses both formats is to bring the commitment earlier by roughly 1,500 words, which strengthens the Kindle margin and rescues the paperback from a miss. Trimming front matter alone cannot rescue a 2,050-word story window when the conflict lives at 6,900.
Now a failure case on a 68,000-word literary novel with heavy opening context. Total Kindle sample is 6,800 words. Front matter is 1,100 words, so story words are 5,700. Chapter 1 alone runs 3,800 words. The inciting incident, defined as the afternoon the narrator decides to leave, sits at word 9,200; the central conflict — what leaving will cost — arrives at word 12,400. Even the opening of the incident is 3,500 words beyond the sample, and Chapter 1 consumes two thirds of the preview before any turn arrives. The tool reports a fail with a margin of minus 3,500. Moving the incident to word 5,200 requires cutting roughly 4,000 words of scene-setting before it. That is a major revision. Trimming front matter from 1,100 to 350 would gain only 750 words and would not change the verdict. This is the pattern where the sample diagnostic saves months of blind revision: without the boundary, an author might tighten sentences when the actual task is to resequence the first act.
Edge cases the tool handles explicitly
A very short book, under 25,000 words, generates a small Kindle sample. A 20,000-word business lead magnet gets a 2,000-word window, of which front matter can consume more than half. Many sub-25k books will always show a fail for the central conflict, not because they are poorly structured but because the sample budget is smaller than the distance between beats. The prescription for a short book is to deliver both beats inside a tight window: place the incident before word 1,500 and make the promise explicit by word 2,000, and keep front matter under 300 words. Treat the sample as the whole sales page for brevity.
A very long book, above 120,000 words, generates a large Kindle sample — 12,000 to 15,000 words — which comfortably covers two beats that a shorter book would miss. Long books often pass Kindle easily and still fail print, because 2,750 words is a fixed ceiling. Do not assume a pass on Kindle means the paperback preview is safe. Run the toggle and check print separately.
Nonfiction, memoir, and how-to structures rarely have a single inciting incident. For these, define the incident as the first place a reader encounters evidence that her current approach is costly and an alternative exists. That is usually the opening story or the failed attempt the book will fix. The central conflict is the articulation of the method — the point where a reader can name what she will learn. Use those two anchors and the same arithmetic applies even though the prose is not narrative.
Collections and multi-POV epics raise a placement question across stories. If the strongest hook lives in story two, the sample may contain none of it. When that distance is large, consider an ordering change or a framing prologue that signals the book's range early.
How to measure word positions without guessing
Guessing defeats the purpose. Measure from byte one of the upload file.
In Scrivener, select from the first document through the beat and read Project Statistics for the selection. In Word, use a contiguous selection from character one through the incident and read the status bar count, or sum split documents and subtract front matter. In Google Docs, use Tools then Word count on the full selection or export to DOCX for large files. In Vellum or Atticus, count the source file before typesetting, because PDF ornaments do not change the uploaded word count. Always verify you counted from the file start, not Chapter 1.
Cross-check that your total measured words match Amazon's ingestion count within one percent. If the sum differs, you counted a subset. Keep a dated note file with total words, front matter, Chapter 1 length, incident word, and conflict word alongside your KDP metadata so revisions compare apples to apples.
Common mistakes and how to avoid them
Counting from Chapter 1 rather than from the first page of the file is the most frequent error, and it always produces an answer that is too optimistic. Add front matter to every count even if you think Word excluded it.
Assuming print and digital behave alike is the second. Authors who verify their opening on Kindle and never check the print preview routinely ship paperbacks whose Look Inside stops before the story starts. The remedy is not to memorize two numbers but to re-run the tool with the format toggle and to open both previews yourself before launch.
Treating the sample as a hook problem when it is a placement problem is the third. A strong first line does not help if the turn it promises never arrives inside the preview. The sample is a budget, not a voice exercise.
Loading the front with endorsements before the first chapter is a fourth. Three pages of blurbs feel reassuring to the author and read as filter to a new reader who has not yet decided to trust the book. Move endorsements to the back matter, where Amazon never shows them in the sample and where a committed buyer will actually read them.
Including an uncompressed table of contents with leader dots and full chapter titles at length is a fifth. In preview it renders as a wall of non-story text that pushes the story start further into the window. If your genre requires a contents page, keep it tight or allow Kindle to generate navigation separately.
Opening with a prologue that is technically story but functionally preamble is a sixth. A 2,000-word prologue set in another time or place delays the incident if the incident lives in Chapter 1. Either compress the prologue so both beats still fit, or confirm the prologue itself contains the incident and measure from its first word accordingly.
Editing only line craft is a seventh. The sample is measured in words; removing a thousand words of setup is worth more than polishing a thousand words of setup.
How to verify the result live on Amazon
Before you publish, use KDP's previewer to turn the dial yourself. Upload the file, open the previewer, and page forward until the preview ends for both Kindle and paperback. Note the last visible line of text and compare it to your manuscript position. Does the preview end where the arithmetic predicted? Are there images or tables that shifted the budget compared to a pure word count? Adjust the front matter measurement until the preview and the tool agree within a few hundred words.
After publication, open the live Amazon page in an incognito window. On Kindle use Send a sample; on paperback use Look Inside from the cover thumbnail. Scroll to the end. The final words should match your boundary within about 500 words. If they differ more, recount front matter and incident positions; an off-by-one chapter is usually the cause.
Mobile and desktop samples should agree for eBook, but print preview can vary slightly between Cloud Reader and the paperback page. Test both and use the shorter number as the constraint.
Final checklist before you ship
Before you lock the file, run this sequence and record answers alongside your KDP metadata.
Confirm the production file's total word count and the front matter word count measured from byte one through the last word before Chapter 1. Write down both and the difference — story words in the sample.
Mark the inciting incident's start word and the central conflict's start word measured from the same origin. Record whether each is visible in the Kindle sample and in the print preview, with the margin to the boundary.
Verify the verdicts. A thin pass on Kindle with less than 500 words of margin and any fail on print should block launch until at least front matter is trimmed. A near-miss warning is the most common blocking state and the one most worth fixing before spending on cover and ads.
Open KDP previewer for both formats and confirm the last visible word matches the tool's prediction within a few hundred words.
Open the live listing incognito after publication and confirm the real sample ends where you expected. If it does not, recount front matter and incident positions using the live file, not memory.
Save the note file with the date. When you revise, compare new numbers to old ones rather than relying on the feeling that the opening is now tighter.
When not to optimize for the sample
Not every book should chase a sample pass at the expense of its opening. Literary novels that build deliberately, books whose inciting incident gains power because it arrives late, and nonfiction that establishes voice before making a claim may reasonably accept a warning or even a fail if the late beat is essential to the work. In that case, the sample problem is real but the remedy may be to accept the tradeoff eyes open rather than to distort the book. Write the diagnostic down, decide not to move the incident, and invest the promotion spend in an audience that already trusts slower openings — newsletter readers, review copies, and category audiences where the preview is less decisive than the recommendation.
The sample set the number of words Amazon will show a buyer who has not yet paid you. Measure it accurately, fix the cheapest lever first, and know what you chose not to fix.