7 Book Launch Mistakes First-Time Self-Published Authors Make
Most launch problems are avoidable. Here are seven common mistakes first-time authors make and how to avoid each one.
Read article
Trim size is the decision most KDP authors make too fast and regret too late. It sets your page count, your printing cost, your royalty on every copy and the first impression your book makes in a reader's hands, and changing it after launch means rebuilding your files.
If you are publishing through Amazon Kindle Direct Publishing, this is one of the first choices you will face, so it deserves a real hour of thought. This guide covers which sizes Amazon supports, which ones suit each genre, and how size, price and royalty work together in 2026.
Key Takeaways
For US paperbacks, 6 x 9 inches is KDP's default and most common trim size, and most genre conventions sit close to it. Size affects printing cost directly, and since June 2025 it also interacts with a two-tier royalty rate that depends on your list price. Choose your size before you format the interior, because switching after publication usually means creating a new edition.
What Trim Size Means on KDP
Trim size is the final width and height of a printed page after the book has been cut at the factory. It is not your Word page size, and it is not your cover size, which also has to include a spine and bleed. When you choose a trim size in KDP, every interior page is built to that size, and your cover template is generated from it together with your page count.
KDP offers a long menu of standard paperback sizes and also accepts custom sizes, as long as the width falls between 4 and 8.5 inches and the height between 6 and 11.69 inches. If you are unsure where to start, 6 x 9 is a safe default, because readers already read it as a proper trade paperback.
Best Book Size by Genre
Match the size readers already expect in your genre. A romance novel printed at 8.5 x 11 feels wrong the moment someone picks it up, even if they cannot say why, while a workbook printed at 5 x 8 leaves no room to write.
Trim sizeBest forWhy it works5 x 8 inShort novels, poetry, memoirsFeels like a mass-market paperback and keeps a short manuscript from looking thin5.5 x 8.5 inFiction, narrative nonfictionSits comfortably in one hand with a mainstream look6 x 9 inBusiness, self-help, nonfiction, many novelsThe standard trade paperback and KDP's default size7 x 10 inTextbooks, how-to guides, referenceGives diagrams and tables more room8 x 10 inWorkbooks, journals, picture booksSpace to write or show images for less than letter size8.5 x 11 inManuals, planners, large workbooksMatches US letter paper, so pages print and tear cleanly
For a novel of 60,000 to 90,000 words, 5.5 x 8.5 or 6 x 9 almost always works. Picture books often use square formats such as 8.5 x 8.5, because the shape gives illustrations space. Very short books and poetry look more intentional in the smaller sizes, where a thin spine still feels deliberate.
A quick way to confirm your choice is to open the top ten bestsellers in your category on Amazon and read the dimensions on each product page. If eight of them share a size, that is your answer.
How Trim Size Affects Printing Cost and Royalty
A bigger page does not automatically mean a cheaper book, because KDP charges more per page once a book passes a certain size. Any trim wider than 6.12 inches or taller than 9 inches counts as a large trim size, and large sizes cost roughly $0.015 per page for black and white interiors, against about $0.012 for standard sizes. A 7 x 10 book can therefore cost more to print than a 6 x 9 book even if the bigger page cuts your page count.
Since June 10, 2025, your list price also decides which royalty rate you earn. KDP now pays 60% on paperbacks and hardcovers priced at or above a marketplace threshold and 50% on books priced below it. On Amazon.com the line is $9.99, and other marketplaces use their own thresholds in local currency, so one book can earn 60% in one country and 50% in another.
Here is what that looks like in practice. Take a 300-page paperback with a $4.60 printing cost, which is the example Amazon itself uses. Priced at $9.98, it earns 50% of the list price minus printing, which is about $0.39 per copy. Priced at $9.99, it earns 60% minus printing, which is about $1.39. One cent changes your income per sale by a full dollar.
KDP also enforces a minimum list price equal to your printing cost divided by your royalty rate. With that same $4.60 cost, the minimum is $7.67 at the 60% rate and $9.20 at the 50% rate. So a large trim is not a bad choice in itself: an 8.5 x 11 workbook at $14.99 can earn well, while a short novel in a large trim at $8.99 can earn almost nothing. Plan size, page count and price together, and test them in KDP's printing cost and royalty calculator before you upload anything.
Hardcover Sizes: Pick One That Works for Both Formats
If you may publish a hardcover later, choose a trim size that both formats support, because KDP's hardcover menu is much shorter than its paperback menu. Current hardcover options include 5.5 x 8.5, 6 x 9, 6.14 x 9.21, 7 x 10 and 8.25 x 11 inches. Staying inside that list lets you reuse the same interior file instead of reformatting from scratch.
Hardcovers also cost more to print than paperbacks of the same length, so their list price has to be higher to leave a meaningful royalty. Decide on your hardcover size now, even if the edition comes months later.
Formatting Details That Depend on Your Size
Once your size is chosen, your files have to match it exactly. For an interior PDF with bleed, the page width is the trim width plus 0.125 inches and the page height is the trim height plus 0.25 inches. Without bleed, the page size equals the trim size. Do not add crop or trim marks, because KDP handles trimming during production.
Keep text and artwork well inside the margins, and widen the inside margin as your page count grows, since thicker books curve more near the spine. Test one real chapter at actual size before you format the whole manuscript, because a font that looks fine on screen can feel cramped on a 5 x 8 page.
Spine text has a limit too. KDP requires at least 79 pages before you can place text on a paperback spine, so a shorter book needs a clean, text-free spine.
Can You Change Trim Size After Publishing?
Not on a live book. You can publish a new edition in a different size, but the interior must be reformatted and the cover rebuilt for the new dimensions, and the new edition has to be linked properly if you want to keep your reviews and listing history.
That is why it pays to decide once. Spend an afternoon checking bestsellers in your genre, run two sizes through the cost calculator, order a proof copy of your favorite, and only then lock the interior.
Where Book Size Fits in Your Bigger Plan
Book size is one small piece of a bigger publishing plan, and the control it gives you is one of the real Amazon self publishing pros. You can test sizes, order proofs and fix mistakes without waiting for a publisher's approval. A well-chosen size will not sell the book on its own, though, so give your launch as much planning as your manuscript, starting with a steady book marketing routine.
If you are also deciding how to reach readers who prefer subscriptions or audio, our comparison of Audible vs Kindle Unlimited will help you choose your next format.
FAQs
What is the most common KDP paperback size?
6 x 9 inches is KDP's default and the most common choice, especially for nonfiction and many novels.
Can I use a custom trim size?
Yes, within KDP's width and height limits for paperbacks. Standard sizes are safer for cost estimates and reader expectations, so use a custom size only when you have a clear reason.
Does a bigger book size cost more to print?
Usually, yes. Large trim sizes carry a higher per-page rate, although a larger page can lower your page count, so compare both sizes in the calculator.
Are hardcovers available in every size?
No. Hardcover supports a shorter list than paperback, so confirm your size is on it before you design the interior.
Are these numbers fixed?
No. Printing costs, royalty thresholds and page limits can change, so confirm the current figures in KDP's calculator and help pages before you publish.