Last reviewed by Robert Prime — May 2026
Quick Answer: Your file is above KDP's 650MB cap (or 50MB for Kindle reflowable EPUBs). Reduce file size: optimise images (target 300 DPI at print size), embed only used font subsets, remove unused metadata, run Acrobat's 'Reduce File Size' preset.
Full reasoning, why-it-happens, and the exact fix below.
UK note: UK-specific considerations apply — ISBN purchases go through Nielsen (not Bowker), VAT rules differ from the US (print books are zero-rated; ebooks carry 20% VAT), and GDPR applies to any email/customer data. See our UK self-publishing guides for specifics.
We see this come through our formatting queue at publishing.co.uk regularly, so the patterns and fixes here are based on what actually works at upload.
What this error means
KDP enforces a 650MB upper limit on both paperback interior PDFs and Kindle EPUB files. Files larger than 650MB either fail to upload outright or are rejected after upload with "Your file exceeds the maximum file size limit."
Most novels are well under this — a 300-page text-only paperback PDF is typically 1–5MB. The limit only bites for image-heavy books: photo books, cookbooks, illustrated children's books, art books, and academic books with hundreds of figures.
For Kindle, KDP also charges a delivery fee of $0.15 per MB (US, 70% royalty tier) above 1MB. Even at 5MB your royalty per sale drops by ~$0.75. So there's a financial reason to compress beyond just hitting the 650MB ceiling.
📎 Source: KDP's authoritative documentation on this rule is at KDP's file-size limits.
Why it happens
Uncompressed image embedding. Photoshop "Save as PDF" with "Preserve Photoshop Editing Capabilities" embeds full layered PSDs, multiplying file size 5–10×.
TIFF images at 600 DPI when 300 DPI is plenty. TIFFs are lossless and uncompressed; a single page-sized TIFF can be 30MB.
InDesign with linked images set to "High Quality Print" preset preserves images at maximum resolution. Switch to "Press Quality" or "PDF/X-1a" to downsample to 300 DPI.
Font embedding without subsetting. Embedding a full Unicode font (50,000+ glyphs) when you used only Latin characters adds 5–20MB per font.
Picture book EPUBs. Reflowable EPUB with high-res illustrations can exceed 100MB; fixed-layout EPUB (children's, cookbook) can easily hit 300MB+.
Embedded videos or interactive elements in EPUB. KDP doesn't support video — strip them out.
Multiple language editions packed in one file, or one EPUB containing both Latin and CJK glyphs in every font.
The fix
Step 1: Confirm file size. Right-click → Properties (Windows) or Get Info (Mac).
Step 2 (PDF: Acrobat compression). Open in Acrobat → File → Save As Other → Reduced Size PDF or Compressed PDF. Choose "Acrobat X and later" compatibility. This downsamples images to 150–300 DPI and strips redundant data. Test the output — can lose quality if pushed too far.
Step 3 (PDF: targeted image compression). Acrobat → Tools → Optimise PDF → Audit Space Usage. See which page elements are biggest. Images is usually #1, fonts #2.
Step 4: Re-export from source with compression. (InDesign): File → Export → PDF/X-1a:2001 → Compression tab → set colour images to 300 DPI, downsample using "Bicubic Downsampling", compression "JPEG", image quality "Maximum". For greyscale, same settings. Monochrome can go to 1200 DPI with CCITT Group 4 (lossless).
Step 5 (Photoshop image compression before placing). Open each large image → Image → Image Size → 300 DPI at print dimensions → Save As → JPEG Quality 9 (high but not max). Re-place in your manuscript.
Step 6 (Font subsetting). In InDesign → File → Export → PDF → Advanced → Fonts → "Subset fonts when percent of characters used is less than" → set to 100% (forces full subsetting). Cuts font weight to roughly 5–10% of original.
Step 7 (EPUB: image compression). Open in Sigil → Tools → Image Information → list shows file size per image. Compress large ones externally (use Squoosh or ImageOptim) then replace in Sigil.
Step 8 (EPUB: strip video and audio). KDP doesn't support video or audio in Kindle EPUB. Open the EPUB folder → delete any .mp4, .mp3, .ogg, .webm files → remove their references from the manifest.
Step 9: Re-verify file size. Aim for well under 650MB — ideally under 50MB for EPUB to keep delivery fees low.
How to pre-flight it
Our free KDP Readiness Score reports your file size, the size of the largest images, and an estimated delivery fee for Kindle. Plus 30+ other KDP rules in one pass.
Related errors
- KDP error: low-resolution interior images
- KDP error: embedded images too large
- KDP error: transparency not flattened
FAQ
Does the 650MB limit apply to both PDF and EPUB? Yes — 650MB is the cap for both print PDF interiors and Kindle EPUB uploads.
Will compressing images affect print quality? At 300 DPI JPEG Quality 9, no visible quality loss for photographs. Line art and diagrams should stay as vector or higher-DPI to avoid jagged edges.
Is there a smaller limit for fixed-layout Kindle? The 650MB upload limit applies, but fixed-layout files compress less efficiently. Many children's book EPUBs hit 50–200MB legitimately.
Why is Kindle delivery fee a thing? It covers Amazon's bandwidth to push the file to customers' devices. The fee only applies on the 70% royalty tier (35% tier has no delivery fee but a much lower royalty).
Frequently asked questions
How do I check my current file size before uploading?
Right-click the file → Properties (Windows) or Get Info (Mac). Compare to KDP's limit for your format. Use our free KDP Readiness Score to verify everything is within spec before submitting.
How do I find which part of my file is over KDP's size limit?
Acrobat → Tools → Optimize PDF → Audit space usage shows the byte breakdown by content type (images, fonts, structure). Almost always the answer is one or two hero images that need down-sampling. The fix is rarely structural.
Can publishing.co.uk compress my PDF without visible quality loss?
Yes — we use Acrobat's PDF/X-1a:2001 optimisation profile with image down-sampling to 300 DPI at output size. This typically reduces file size by 50-70% with no visible quality loss in print. Files routinely go from 200 MB to 40 MB.
Does smaller file size affect print quality?
Not if the compression is done with appropriate settings. The trap is using aggressive web-compression settings on a print file — that produces visible artefacts. Print-tuned compression (300 DPI down-sampling, ZIP for line art, JPEG quality 85 for photos) preserves print fidelity.
Related KDP error fixes
If you got the rejection above, you may also want to check these related issues — they tend to cluster:
Full list: KDP formatting errors hub · KDP rejection fixes hub · KDP rejected my book
About this guide
This page is part of a series of UK-focused KDP rejection guides at publishing.co.uk, each documenting a specific reason KDP can reject a print or Kindle file and the exact fix. Written by Robert Prime — founder of publishing.co.uk, co-runs the LoveReading network, and has overseen 500+ KDP submissions through formatting work in this category (file size).
If you'd rather have someone else handle this and the other 35 issues KDP checks for, our formatting service is from £69 with a 3-day turnaround and a 100% KDP-acceptance guarantee.
Run a free KDP Readiness Score on your file before you upload — catches this issue and 35 others, in 60 seconds.
External references
- Amazon KDP Help — official KDP documentation
- Author Earnings reports (ALCS) — UK author income surveys
