Amazon KDP Technical Setup: Fix Common Errors

Last reviewed by Robert Prime — May 2026

Table of Contents

• Introduction
• What You Need to Know Before Starting
• How to Prepare Your Interior File for KDP
• How to Fix KDP Cover Spacing and Sizing
• How to Set Up Series Numbering on KDP
• UK-Specific Considerations
• Common Mistakes and How to Avoid Them
• Tools and Resources for UK Authors
• Expert Tips from 25 Years in the Industry
• Frequently Asked Questions

Introduction

KDP looks simple until you're inside it. The dashboard is clean, the upload steps seem logical — and then something breaks. A cover gets rejected. The interior looks wrong in the previewer. Your series number never appears on the product page. I've been there.

When I was preparing Google. Panic. Repeat. for publication, I assumed my two decades of e-commerce experience would make the technical side of KDP straightforward. It didn't. The margin specs caught me out. The cover template confused me. The series field defeated me for longer than I care to admit. That frustration is precisely why I built publishing.co.uk — to give UK authors a straight answer instead of a fragmented help centre.

This guide covers the three technical areas that generate the most KDP rejections and errors: interior file preparation, cover image sizing and spacing, and series metadata. Every number in here is verified against KDP's current specifications as of May 2026. I've stripped out the guesswork and given you the exact figures, the correct sequence, and the edge cases that catch people out even after they think they've got it right.

TL;DR — Key Takeaways

• KDP accepts EPUB (recommended), DOCX, KPF, HTML, RTF, and TXT for ebooks; PDF and DOCX for print. MOBI was discontinued on 18 March 2025.
• Gutter margins are tiered by page count — from 0.375" (under 150 pages) up to 0.875" (700+ pages). Getting this wrong is the single most common interior rejection trigger.
• Ebook cover images must be a minimum of 1,000 × 625 px; the recommended size is 2,560 × 1,600 px in JPEG or TIFF, RGB, at 300 DPI.
• Spine width for print covers is calculated using a formula based on page count and paper type — it is not a fixed number, and you must recalculate it for every edition.
• Series numbering must be entered in KDP's dedicated Series field, not the title or subtitle. The series name must be character-for-character identical across every edition, and the series number must be digits only (e.g. "1", not "Book 1").
• KDP's standard review time is up to 72 hours; low-content books (journals, notebooks) can take up to 10 business days.

What You Need to Know Before Starting

KDP's technical requirements cover three distinct areas — interior files, cover images, and metadata — and errors in any one of them can delay or block publication. The most important thing to understand before you upload anything is that KDP's specifications are not suggestions: they are hard limits, and the system will reject files that fall outside them, sometimes without a clear error message explaining why.

For interior files, KDP accepts EPUB (recommended), DOC/DOCX, KPF (Kindle Create), HTML, RTF, and TXT for ebooks, and PDF (recommended) or DOCX for print. MOBI was discontinued by KDP on 18 March 2025 and is no longer an accepted upload format — if you have older guidance telling you otherwise, discard it. For print, the critical variables are trim size, margin settings, and font embedding. For ebook, the critical variable is reflowable structure: Kindle devices reflow text to fit the reader's chosen font size, so fixed-layout assumptions from your Word document will not survive conversion intact.

Cover images have separate requirements for ebook and print. Metadata — including series information — lives in a different part of the KDP dashboard entirely, and the rules there are strict in ways that aren't obvious from the interface.

Before you touch any file, read the KDP formatting checklist and confirm your trim size using the KDP trim size guide. Those two steps alone will prevent the majority of first-submission errors.

How to Prepare Your Interior File for KDP

The interior file is the most technically demanding part of KDP setup. For print, you need a PDF or DOCX built to exact margin and bleed specifications that vary by page count and trim size. For ebook, you need a clean reflowable file — ideally EPUB — with embedded structure rather than visual formatting. The single most common cause of interior rejection is incorrect gutter (inside) margins: KDP uses a tiered system based on page count, and the margins that look fine on screen are often too narrow for the physical binding.

KDP's gutter margin requirements for print are as follows: under 150 pages requires a minimum 0.375" gutter; 151–300 pages requires 0.5"; 301–500 pages requires 0.625"; 501–700 pages requires 0.75"; and 700 or more pages requires 0.875". Outside, top, and bottom margins must be at least 0.25" for non-bleed content, or 0.375" where bleed is used. If your book has full-bleed interior images, you'll also need 0.125" (3 mm) bleed on all outer edges, and your PDF must be exported with bleed marks — a workflow that Word cannot handle reliably.

Use the KDP margin calculator to get the exact figures for your page count before you build your file.

Step 1 — Set Your Trim Size First

Decide your print trim size before you set a single margin. Common UK fiction trim sizes are 129 × 198 mm (B-format paperback) or 198 × 129 mm landscape. US trade paperback is 6 × 9 inches, which is widely used by UK authors publishing to Amazon's global marketplace. Download KDP's print template for your chosen trim size from the KDP help centre before you begin formatting — building to the template is far more reliable than trying to match specs manually after the fact.

Step 2 — Set Margins Using KDP's Tiered Requirements

Apply the gutter margins from the table above. Set your outside, top, and bottom margins to at least 0.25" (non-bleed) or 0.375" (with bleed). Mirror margins must be enabled so the gutter alternates between left and right pages correctly. In Microsoft Word: Layout → Margins → Custom Margins → tick Mirror margins.

If you want a visual reference for how trim size affects the finished book, the trim size visualiser is worth a few minutes of your time before you commit to a size.

Step 3 — Embed All Fonts

In Word: File → Options → Save → tick Embed fonts in the file. In Adobe InDesign: export PDF with Include All Fonts selected. KDP will substitute any font it cannot find, and the substitution is rarely what you intended. This is a particularly common problem with decorative chapter-heading fonts.

Step 4 — Export as PDF/X-1a for Print

This format flattens transparency and locks colour profiles. Use CMYK colour mode, not RGB, for print interiors. For ebook files, RGB is correct — do not apply CMYK to ebook uploads.

Step 5 — Use KDP's Previewer Before You Submit

Upload your file to KDP, then open the print previewer before you click publish. Check every page. Pay particular attention to chapter openers, headers and footers, and any images. A file that looks correct in Word will sometimes reflow or shift in KDP's rendering engine, and it is far easier to fix before publication than after. For a full walkthrough of the upload process, see how to upload a book to KDP.

How to Fix KDP Cover Spacing and Sizing

Cover errors are the second most common cause of KDP rejection, and they split into two distinct problems: ebook covers that display with white bars on Kindle devices, and print covers where the spine width is wrong. Both have precise fixes. For ebook covers, the minimum accepted size is 1,000 × 625 px, but the recommended size is 2,560 × 1,600 px — a 1.6:1 ratio — in JPEG or TIFF format, RGB colour mode, at 300 DPI. White bars on Kindle devices are almost always caused by transparent or white padding inside the image file itself, not by the image dimensions.

For print covers, the spine width is not a fixed number. KDP calculates it using a formula based on page count and paper type. For white paper: multiply your page count by 0.002252 inches. For cream paper: multiply by 0.0025 inches. For standard colour paper: multiply by 0.0032 inches. For premium colour paper: multiply by 0.002347 inches. Add the spine width to your front and back cover widths, then add 0.125" bleed on all four outer edges. Books under 79 pages cannot carry spine text at all. The spine width calculator will do this arithmetic for you — use it every time, because even a small error here causes the cover to be rejected or the spine text to be trimmed.

Fixing Ebook Cover White Bars

Open your cover file in Photoshop, Affinity Photo, or an equivalent editor. Check the canvas size — it should be exactly 2,560 × 1,600 px with no transparent border. If there is any padding, crop it out or extend the design to fill the full canvas. Export at exactly 2,560 × 1,600 px as a JPEG (maximum quality) or TIFF. Do not add padding inside the file. The image must fill the canvas edge to edge.

For a detailed walkthrough of cover design requirements, the KDP cover formatting guide covers every variable including safe zones and text placement.

Fixing Print Cover Spine Width

1. Go to your book in KDP → Cover → Download a cover template. Enter your trim size and page count. KDP generates a template file with guides already placed for front cover, spine, back cover, and bleed.
2. Place the template as a background layer in Photoshop or Affinity Publisher. Design within the guides. Keep all critical text and imagery at least 3 mm inside any guide line — this is the safe zone.
3. If you are publishing both a paperback and a hardcover edition, generate a separate cover template for each. The spine calculation formula differs between the two formats, and a cover built for one will not work for the other.
4. Export as PDF or JPEG at 300 DPI in CMYK colour mode.

If you are building your cover from scratch rather than adapting an existing design, the KDP cover template guide explains the full process.

How to Set Up Series Numbering on KDP

Series numbering on KDP is handled through a dedicated metadata field in the book details section — not through the title, subtitle, or description. When it works correctly, Amazon displays a series badge on your product page and groups your books together automatically. When it fails, the most common cause is a mismatch between the series title as entered on different books in the series, or series information placed in the wrong field entirely.

The series name must be character-for-character identical across every edition — Kindle, paperback, and hardcover. "The Ashford Chronicles" and "Ashford Chronicles" are treated by Amazon's system as two entirely different series. A single extra space, a different capitalisation, or a missing article will break the link. The series number must be digits only: enter "1", not "Book 1", not "One". KDP formats the display automatically once the number is in the correct field. Review time for series metadata to appear on the product page is typically 24–72 hours after the change is saved; if the badge has not appeared after 72 hours, check every book in the series for a mismatch.

Step-by-Step Series Setup

1. In KDP, go to your book's details page. Under Book Details, scroll to the Series section — it sits below the description field and above keywords.
2. Enter the series title exactly as you want it to appear. Use consistent capitalisation and punctuation across every book in the series.
3. Enter the series number as a digit only: 1, 2, 3. Do not type "Book 1".
4. Save and republish. The series badge can take up to 72 hours to appear on your Amazon product page.
5. Repeat for every book in the series, using the identical series title string each time.
6. Do not put series information in your title or subtitle fields. KDP's content guidelines flag this, and it can suppress your book from search results.

If your books are still not grouping correctly after 72 hours and you have verified the series title matches exactly, contact KDP support directly — there is occasionally a backend linking issue that requires manual intervention.

UK-Specific Considerations

UK authors face a handful of technical and commercial considerations that do not apply in the same way to US-based self-publishers, and the most significant of these is ISBN management. In the UK, ISBNs are issued exclusively by Nielsen Book Services via nielsenisbnstore.com. A single ISBN costs £89 plus VAT at the standard rate. A block of 10 ISBNs costs £164 plus VAT — substantially better value per unit if you are publishing more than one or two titles. These prices reflect the May 2026 tariff; check the Nielsen store directly for the current rate before purchasing.

KDP offers a free ISBN for print books, but that ISBN lists Amazon as the publisher of record. This matters for UK authors who want their books stocked by Waterstones, Foyles, or Blackwell's, or distributed through UK wholesalers Gardners and Bertrams via IngramSpark — all of which require a publisher-owned ISBN, not a KDP-assigned one. If UK bookshop distribution is part of your plan, purchase your own Nielsen ISBN before you set up your KDP listing. For a full breakdown of ISBN requirements and when you need your own, see ISBN requirements UK.

VAT treatment also differs by format. Printed books are zero-rated for VAT in the UK, which makes print pricing more straightforward. Ebooks sold via Amazon UK are subject to VAT at the standard rate, but Amazon handles the collection and remittance — you do not need to register for VAT solely because of ebook sales through KDP. For broader tax questions around self-publishing income, the self-publishing tax guide for UK authors covers the key HMRC obligations.

If you are considering distribution beyond Amazon, KDP vs IngramSpark sets out the practical differences for UK authors, including how the two platforms handle UK wholesaler relationships.

Common Mistakes and How to Avoid Them

Mistake 1 — Uploading MOBI Files for Kindle

MOBI was discontinued by KDP on 18 March 2025. Authors who still have MOBI in their workflow — from older formatting guides or saved templates — will find their upload rejected. KDP now accepts EPUB (recommended), DOCX, KPF, HTML, RTF, and TXT for ebooks.

How to avoid: Update any saved formatting workflow to output EPUB. If you are unsure which format to use, EPUB vs MOBI: what to upload to KDP in 2026 explains the current position clearly.

Mistake 2 — Using a Single Margin Setting for All Page Counts

A 0.5" gutter is correct for a 200-page book but too narrow for a 400-page book, which requires 0.625". Authors who set margins once and reuse them across titles of different lengths will eventually get a rejection they cannot explain.

How to avoid: Check the gutter tier for every new title. Use the KDP margin calculator each time rather than copying settings from a previous project.

Mistake 3 — Resizing the Cover Inside KDP's Interface

Uploading a cover at the wrong dimensions and relying on KDP to scale it down does not produce the same result as uploading at the correct size. KDP's scaling introduces artefacts, and the result often fails the quality check.

How to avoid: Build and export your cover at the exact required dimensions before upload. For ebook covers, that means 2,560 × 1,600 px. For print, use the template KDP generates for your specific trim size and page count.

Mistake 4 — Putting Series Information in the Title Field

"The Ashford Chronicles Book 1: The Reckoning" as a title field entry is a content guidelines violation. KDP flags it, and it can suppress your book from search results or trigger a rejection.

How to avoid: Enter only the book title in the title field. Use the dedicated Series field for series name and number.

Mistake 5 — Inconsistent Series Title Strings Across Editions

Publishing the Kindle edition with "The Ashford Chronicles" and the paperback with "Ashford Chronicles" means Amazon treats them as separate series. The books will not group together on your author page or product listings.

How to avoid: Copy and paste the series title from one edition to the next — do not retype it. Check every edition (Kindle, paperback, hardcover) for an exact match, including spaces and punctuation.

Mistake 6 — Ignoring the Print Previewer

Authors who upload and publish without checking the print previewer frequently discover formatting errors — misaligned headers, images that have shifted, or page numbers that have collided with content — only after physical proof copies arrive.

How to avoid: Use KDP's print previewer on every upload, zoom to 100% and higher, and check chapter openers, headers, and any pages containing images. Order a physical proof copy before approving distribution.

Mistake 7 — Using DOCX for Complex Ebook Layouts

KDP's DOCX-to-Kindle conversion handles straightforward prose well. It does not handle drop caps, custom fonts, tables, poetry layouts, or anything that relies on precise visual positioning. The conversion will mangle these elements in ways that are difficult to predict and harder to fix after the fact.

How to avoid: For any book with complex interior formatting, build and upload a properly structured EPUB. The guide to formatting an ebook for Kindle covers the EPUB build process for authors who have not done it before.

Mistake 8 — Not Accounting for Bleed on Interior Images

Full-bleed interior images require 0.125" (3 mm) bleed on the relevant edges, and the PDF must be exported with bleed marks. Word cannot produce this reliably. Authors who attempt full-bleed interiors in Word will either get a rejection or end up with white slivers at the page edge.

How to avoid: Use InDesign, Affinity Publisher, or a purpose-built formatter for any book with full-bleed interior images. If you are unsure whether your file is set up correctly, the KDP readiness audit will flag bleed issues before you submit.

Tools and Resources for UK Authors

For a broader comparison of formatting software options, best book formatting software covers the main tools with UK pricing. If you want a free option, best free open-source tools for self-publishers includes GIMP, Calibre, and Sigil.

KDP's own help documentation is the authoritative source for specification changes. The KDP help centre covers interior file requirements, cover templates, and metadata rules — bookmark it and check it when you are working to a new trim size or format, because specs are updated without announcement.

Expert Tips from 25 Years in the Industry

Build a master template and protect it. Every time I start a new title, I open a master InDesign template that already has the correct margins, trim size, bleed settings, and font embedding configured. I never start from a blank document. The template took half a day to build properly and has saved me hours on every subsequent project. If you are using Word, save a correctly configured .dotx template file and use it as your starting point every time.

Recalculate the spine for every edition, every time. I have seen authors use the same cover file for a paperback reprint after adding a foreword, not realising the page count had changed enough to shift the spine width. The cover was rejected. The spine formula is not complicated — page count multiplied by the paper-type constant — but it must be applied fresh for every version of every book. The spine width calculator takes ten seconds. Use it.

Treat the series field as a database key, not a label. Amazon's series grouping system works like a database lookup: it matches the series title string exactly across all editions. Think of it as a primary key, not a display label. That means you should decide on the exact series title string before you publish the first book, write it down, and copy-paste it every single time. Never retype it from memory.

Order a physical proof before you approve distribution. The print previewer is good, but it is not a substitute for holding the book in your hands under different lighting conditions. I order a proof copy for every new title. The cost is a few pounds and a few days. The alternative — discovering a formatting error after hundreds of copies have been sold — is considerably more expensive in both money and reputation.

If you have had a rejection and cannot identify the cause, start with the margins. In my experience, incorrect gutter margins account for more unexplained KDP rejections than any other single factor. Before you go looking for an obscure technical issue, verify that your gutter margin matches the tier for your actual page count. The KDP formatting errors guide is a useful diagnostic tool if the margin check does not resolve it.

Frequently Asked Questions

What file formats does KDP accept for ebooks in 2026?

KDP accepts EPUB (recommended), DOC/DOCX, KPF (Kindle Create), HTML, RTF, and TXT for ebook uploads. MOBI was discontinued by KDP on 18 March 2025 and is no longer accepted. EPUB gives you the most control over formatting and is the format recommended by KDP for anything beyond simple prose.

What are the correct KDP cover image dimensions?

For ebook covers, the minimum is 1,000 × 625 px, but the recommended size is 2,560 × 1,600 px — a 1.6:1 ratio — in JPEG or TIFF format, RGB colour mode, at 300 DPI. For print covers, dimensions depend on your trim size and page count; use KDP's cover template generator to get the exact file with guides already placed.

How do I calculate spine width for a KDP print cover?

Multiply your page count by the constant for your paper type: white paper × 0.002252", cream paper × 0.0025", standard colour × 0.0032", premium colour × 0.002347". Add the result to your front and back cover widths, then add 0.125" bleed on all four outer edges. Books under 79 pages cannot carry spine text.

Why is my series number not showing on my Amazon product page?

The most common cause is a mismatch in the series title field between editions — even a single extra space or different capitalisation breaks the link. Check that every edition (Kindle, paperback, hardcover) has the identical series title string. Also confirm the series number is entered as a digit only ("1", not "Book 1"). Changes can take up to 72 hours to appear.

Do I need my own ISBN to publish on KDP in the UK?

You do not need your own ISBN to publish on KDP — Amazon will assign a free ASIN and a free KDP ISBN for print books. However, the free KDP ISBN lists Amazon as publisher of record, which prevents distribution through UK bookshops (Waterstones, Foyles, Blackwell's) and UK wholesalers (Gardners, Bertrams via IngramSpark). If you want distribution beyond Amazon, purchase a Nielsen ISBN from nielsenisbnstore.com before setting up your listing. A single ISBN costs £89 plus VAT; a block of 10 costs £164 plus VAT.

How long does KDP take to review a submitted book?

Standard books take up to 72 hours. Low-content books — journals, notebooks, planners — can take up to 10 business days. You will receive an email when your book is live or if there is a problem with your submission.

Can I use the same cover file for my paperback and hardcover editions?

No. KDP uses a different spine width formula for hardcovers than for paperbacks, so the spine dimensions will be different even for the same page count. Generate a separate cover template for each edition via the KDP dashboard.

What is the difference between an ASIN and an ISBN?

An ASIN (Amazon Standard Identification Number) is assigned automatically by Amazon to every product listed on its platform, including KDP books. An ISBN is an international identifier required for distribution outside Amazon. In the UK, ISBNs are issued exclusively by Nielsen Book Services. If you want your book available through non-Amazon retailers or wholesalers, you need your own ISBN — the ASIN alone is not sufficient.

My KDP file was accepted but the interior looks wrong in the previewer. What should I check first?

Check your gutter margins against the tier for your actual page count. Then check font embedding. Then check whether any images have shifted from their intended position. The KDP quality check failed guide covers the full diagnostic sequence if those three checks do not resolve the issue.

Is DOCX or EPUB better for Kindle uploads?

For straightforward prose fiction or non-fiction with standard chapter formatting, DOCX is manageable. For anything with complex formatting — drop caps, custom fonts, tables, poetry, or precise visual layout — upload a properly built EPUB. KDP's DOCX conversion handles simple prose well but produces unpredictable results with anything more complex.

About the Author

Robert Prime is a best-selling self-published author, veteran e-commerce strategist, and the founder of publishing.co.uk. With over 25 years of experience in digital business and 15 successful exits, he brings a battle-tested perspective to the publishing industry. After experiencing firsthand the technical headaches of formatting a KDP-compliant book for his own bestseller, Google. Panic. Repeat., Robert built publishing.co.uk to solve the problem for other authors. He is also a co-owner of the LoveReading.co.uk network (the UK's largest book review platform), founder of the Amazon growth agency MrPrime.com, and a member of the Forbes Business Council.