Book Formatting Software for Amazon KDP
The Best Book Formatting Software for KDP in 2026
Five book formatting tools. One question. Which one gets your book into Amazon KDP without a rejection email? We build one of them. We will be honest about where each one fits, and where it does not.
No credit card required. Full features during trial.
By Corey Jackson, developer of Lacuna
Reviewed by Melissa Erin Jackson, author of 15 self-published books
Updated July 22, 2026 · Read about us
Full disclosure
We built Lacuna, one of the tools on this page. We are authors too. Melissa has published 15 books, most of them on KDP. We have been through the rejection-email cycle ourselves. We built Lacuna so we would not have to do it again. If another tool fits your KDP workflow better, use it. We would rather you ship the right book than the wrong one.
What KDP Actually Cares About
Most comparison articles do not separate KDP-specific requirements from general formatting. Here is what Amazon’s pipeline actually checks.
EPUB validation that doesn’t trip on the basics
KDP validates your ebook before it goes live. Files that fail come back with messages like “image references not found” that do not tell you how to fix anything. Look for a tool that runs your EPUB through EPUBCheck (the industry-standard validator) before export. That alone catches most of what KDP would reject.
Print specs: trim, gutter, bleed
KDP paperbacks need the right trim size (5×8, 5.5×8.5, 6×9, and others), the right inside margin (the gutter, the space that disappears into the spine), and the right bleed if you have full-page images. KDP’s gutter checks are unforgiving. The right tool ships KDP-spec defaults out of the box so you do not have to set them.
KDP’s format requirements changed in 2025
As of March 18, 2025, KDP no longer accepts MOBI. Accepted ebook formats are now KPF (Kindle Create’s native format) and EPUB.
Going wide later, or not
Some tools lock you into Amazon. Kindle Create’s KPF format only works on Amazon. Even its EPUB export drops features. If you ever plan to publish on Apple Books, Kobo, Nook, or Google Play Books, pick a tool that produces a portable EPUB you can use anywhere.
KDP Print Specs, in Plain Numbers
The numbers Amazon checks on a paperback, straight from KDP’s own specs. A good tool sets these for you, but it helps to know what they are.
Common trim sizes
| 5 × 8″ | Novels, novellas, poetry |
| 5.5 × 8.5″ | Novels, memoir, non-fiction |
| 6 × 9″ | The most common US size; novels and non-fiction |
| 7 × 10″ | Workbooks, textbooks, illustrated non-fiction |
| 8.5 × 11″ | Workbooks, children’s books, photo books |
Watch the cost line: KDP charges more per page to print any size wider than 6.12″ or taller than 9″ (it calls these “large” trims), which lowers your royalty per sale. Lacuna supports the standard sizes plus custom dimensions.
Bleed
Only needed if images run to the edge of the page. When they do, add 0.125″ to the width and 0.25″ to the height of your trim, so a 6 × 9″ book becomes 6.125 × 9.25″. KDP trims 0.125″ off the top, bottom, and outside as it prints. If one page bleeds, the whole interior has to be set up for it.
Inside margin (gutter) by page count
Outside, top, and bottom margins need at least 0.25″ (0.375″ with bleed).
Specs per Amazon KDP’s published paperback guidelines. Always confirm against KDP when you set up your book.
Side-by-Side: Five Tools for KDP
Lacuna, Vellum, Atticus, Reedsy Studio, Kindle Create. The columns that matter most for Amazon KDP.
| Feature | Lacuna | Vellum | Atticus | Reedsy Studio | Kindle Create |
|---|---|---|---|---|---|
| Pricing | |||||
| Price | $149 | $199.99 / $249.99 | $147 | Free | Free |
| One-time purchase | Free + add-ons | Free | |||
| Platform & Privacy | |||||
| Mac | macOS 13+ | Browser | Browser | ||
| Windows | Browser | Browser | |||
| Works offline | Writing only | ||||
| Files stay on your computer | |||||
| KDP Output | |||||
| KDP paperback (print-ready PDF) | PDF/X-1a | PDF/X-1a | PDF/X-1a | PDF/X-1a:2001 | KPF only |
| KDP ebook (EPUB) | EPUB 3 / 2 | EPUB 3 / 2 | EPUB 3 / 2 | EPUB 3 | Reflowable, with feature loss |
| Hardcover support | Same PDF | Not recommended by KDP | |||
| Portable file (use beyond Amazon) | |||||
| Trim & Margins | |||||
| Trim sizes | Standard + custom | Standard + custom | 17 + custom | Only 4 | Any (auto) |
| Gutter / inside-margin control | Fully customizable | Tunable | Auto | Not surfaced | Not customizable |
| Customization | |||||
| Per-section style overrides | Limited | Limited | |||
| Callout boxes | |||||
| Tables | Limited | ||||
| Image gallery with folders | Limited | ||||
| Editor | |||||
| Live preview | |||||
| Find and replace | |||||
Paperback PDF or Kindle EPUB? When You Need Which
KDP takes two different files for two different formats, and most authors need both.
Paperback and hardcover, a print PDF
Print books upload as a print-ready PDF (ideally PDF/X-1a) with your trim size, gutter, and bleed baked in. This is the file the print specs above apply to.
Kindle ebook, an EPUB
The Kindle edition uploads as an EPUB. KDP accepts EPUB directly, and since March 2025 it no longer takes MOBI. Lacuna exports both the print PDF and the EPUB from the same project. See how Lacuna creates EPUBs.
Why KDP Rejects a File (and How to Avoid It)
The handful of issues behind most KDP rejection emails, and the fix for each.
Trim size mismatch
The PDF page size has to match the trim you pick on KDP. Set the same trim in your formatting tool and in your KDP setup.
Gutter too small for the page count
The inside margin grows with page count. Use the gutter table above so the text near the spine stays readable.
Missing or partial bleed
If any page runs an image to the edge, the whole interior has to be set up for bleed. Half-measures get flagged.
Low-resolution images
KDP wants 300 DPI for print. Low-res images trigger a quality warning and can look blurry in the printed book.
EPUB validation errors
Broken image references and invalid markup are the usual culprits. An EPUB built to pass EPUBCheck clears this on the first try.
The Bottom Line on Each Tool, for KDP
One paragraph per tool. Where each one fits if Amazon KDP is your primary destination.
Lacuna (that’s us)
Lacuna is the best book formatting software for KDP in 2026, and yes, we build it.
- More customization freedom than anything else here: build the book you want, not the book the app allows
- KDP-ready by default on both Windows and Mac (Vellum is Mac-only)
- Print-ready PDFs tuned for KDP and IngramSpark, plus EPUB built to clear KDP’s checks
- Per-section control over gutter, margins, and layout
- $149 one-time with lifetime updates, no subscription
Since we started building Lacuna, almost every feature has come straight from authors asking for it. That is how it ended up with more customization freedom than anything else here.
Vellum
Vellum is a Mac-only formatter tuned for KDP output: PDF/X-1a print profile, KDP-tuned gutter defaults, and ongoing attention to KDP-spec changes. The catch is the platform and the price. Mac only. $199.99 for ebook-only, $249.99 for ebook plus print.
Read our full Vellum comparisonAtticus
Atticus is built for self-publishers and it shows. 17 trim sizes plus custom dimensions, and margin/bleed/gutter math automated for KDP. The tradeoffs are real. It runs in your browser. Your files live on their servers. Some features need the internet. $147 one-time. If those tradeoffs do not bother you, Atticus is a solid KDP tool.
Read our full Atticus comparisonReedsy Studio (formerly Reedsy Book Editor)
Reedsy is free where it matters most: the core editor. Browser-based, EPUB and PDF/X-1a:2001 output, KDP-compatible. The big limit for KDP authors is the trim list. Only four sizes (6×9, 5.5×8.5, 5×8, 4.25×6.87). If your book fits one of them, Reedsy is a real option. If you need royal, large-format, or anything else, you will hit a wall.
Kindle Create
Kindle Create is Amazon’s free formatting tool. It works on Windows and Mac. The catch most listicles miss is that Kindle Create does not export a paperback PDF. It produces a single KPF file that you upload to KDP twice, once as the ebook and once as the paperback. KPF is Amazon-proprietary, so you cannot use that file anywhere else. Hardcover support is limited too. KDP’s own hardcover help page does not recommend it. Fine if you publish only on Amazon and only need a simple ebook. Not formatting software in the broader sense.
Why We Built Lacuna
Melissa has published 15 books. Most of them on KDP. She has been through every kind of rejection. Missing metadata, wrong trim, broken EPUB validation. She knows the cycle.
She used Vellum on her Mac. Every time she tried to share the file with a Windows author friend, the workflow broke. She needed a tool that worked on both platforms, handled KDP right by default, and did not cost as much as a freelance designer.
So she and her brother Corey built one. Lacuna. KDP-ready by default. Windows and Mac. $149 one time.
What Authors Are Saying
Real authors. Real books. Formatted with Lacuna.
I’m a cover designer and interior formatter by profession and run my own small publishing press, so trust me when I say I’m picky and my standards are high. InDesign has always been the only program that formats for print with the level of customization I need. For years, I’ve used it for print and another program entirely for ebooks to get the results I wanted. When I saw Lacuna, I immediately went to check it out and within an hour from having downloaded the trial, I was hooked.
This gives me so much more freedom with print options than other formatting programs like Atticus or Vellum while still making ebooks a breeze. The ability to work from one file and have separate print and ebook settings is a complete gamechanger. I’m still learning my way around the program and loving every second.
JJ Carpenter
The Haunting of Kenmore Asylum
I originally checked out Lacuna because somebody in a KDP publishing group I belong to asked if anyone had tried Lacuna out yet. I published nine other books using a different formatter, but I wasn’t happy with it. I ended up taking a look at Lacuna even though I was pretty much sold on Atticus or Vellum. Once I started diving into Lacuna and saw the ease of use and flexibility, I was absolutely floored. It was a no-brainer, and I purchased Lacuna. Since then the program has only improved. Corey is amazing at fixing things and streamlining processes.
If you take a look at the book that I formatted with Lacuna you will see, it would be pretty difficult to do something like that with one of those other formatting programs. Plus they cost more. In my opinion Lacuna is already the best formatter on the market and only getting better. Thanks, Corey and Melissa, for making this available.
NextGen Victory Press
3-Minute Wrestling Devotionals for Rising Athletes
I tried numerous formatting methods and followed endless instructions from publishing websites, but nothing ever turned out right. Since finding Lacuna, everything has changed. I’ve been able to update all my manuscripts effortlessly and give them the professional look they deserve.
Lacuna helped me perfect one of my most cherished stories, The Magic Globe, and finally present it exactly as I envisioned. It’s truly been a game changer for my author journey.
Samuel Graham Astley
The Magic Globe
Frequently Asked Questions about KDP Formatting
You’re 60 Seconds Away from Formatting Your KDP Book
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