You upload your paperback cover to KDP, and instead of a preview you get an error saying the file is the wrong size and quoting the dimensions KDP expects. It is annoying, but it is almost always easy to fix, because the quoted size tells you exactly what KDP calculated from your book's settings. This guide explains what the message means, how to work out why your cover is off, and how to correct the file. The final section shows how to fix it in Quillen with one setting.
The short answer
A cover size error means the width (or sometimes height) of your cover file does not match the size KDP calculated from your trim size, paper type and page count. Nearly all mismatches come from the page count, because that sets the spine width. Find out which input differs, correct it, and re-export. If you only need the file to match the number KDP quotes, you can set the full cover width directly. In Quillen, tick Override full cover width and enter the width from KDP's message.
What the error is telling you
KDP works out the size it expects like this:
- Width = bleed + back cover + spine + front cover + bleed
- Height = bleed + trim height + bleed
The bleed is 0.125 inch on each side, the back and front covers are each one trim width, and the spine depends on the page count and paper. Because everything else is fixed by your trim size, a difference in width is almost always a difference in spine. When KDP says it expects, for example, 13.200 inches and your file is 13.070, the difference of 0.130 inch is spine.
Step 1: Read the numbers
Note the exact dimensions KDP quotes, and the size of your file. Subtract your width from KDP's width. If the result is a small positive or negative number of hundredths of an inch, that difference is your spine error.
Step 2: Turn the difference into pages
Divide the width difference by the thickness per page for your paper type. For cream paper (0.0025 inch per page), a difference of 0.130 inch is 52 pages. For white paper (0.002252) it is about 58 pages. That tells you whether your page count is off by a handful of pages or by a lot, which points to the likely cause.
| Width difference | Roughly how many pages (cream paper) |
|---|---|
| 0.005 in | 2 pages |
| 0.025 in | 10 pages |
| 0.050 in | 20 pages |
| 0.130 in | 52 pages |
| 0.250 in | 100 pages |
Step 3: Find the cause
| Likely cause | How to check |
|---|---|
| Page count differs from the interior you uploaded | Compare the cover's page count with the count KDP shows after your interior was processed |
| Wrong paper type | White, cream, standard color and premium color have different thickness per page |
| Wrong trim size | A different trim changes both covers' widths, so the error is larger than a spine mistake |
| Missing bleed | The file is exactly 0.25 inch narrower and 0.25 inch shorter than expected |
| Interior edited after the cover was made | Page count changed; recalculate |
| Odd page count | KDP rounds up to an even number |
Check the interior first: KDP shows the page count it counted once the interior has been processed, and that is the number to use.
Step 4: Fix the file
You have two options:
- Correct the input and rebuild. Enter the real page count (and the right paper and trim size), let the tool recalculate the spine, adjust your artwork if needed and export again. This is the right fix when your inputs were wrong.
- Match KDP's number. If you are confident everything else is right and you just need the file to match the quoted width, set the full cover width directly. The spine becomes whatever width is left after the two covers and the bleed. This is a quick fix, but check that the implied page count is close to your real one; if it is far off, something else is wrong.
Step 5: Re-export and re-upload
After changing the file, export a new PDF and upload it again. Look at KDP's previewer to check that the spine text, if any, sits inside the spine and that nothing important falls across a fold. Order a printed proof before you publish.
Prevention
- Finish the interior first, then make the cover.
- Use the page count from the final print PDF, not a guess.
- Choose the paper type before you finalize the spine.
- Recheck the cover size every time you change the interior.
- Keep the cover file name and the interior file name together, with the page count, so you know which cover goes with which interior.
Do it in Quillen
Quillen's paperback cover tool calculates the full size from your trim, paper and page count. If KDP quotes a different width, you can set it directly.
- Open your book, click Cover, and choose Paperback cover. Your design reopens with the sizes in the panel on the left.
- First, check the inputs. Look at Trim size, Paper / ink and Page count. If any is wrong, fix it and look at the Spine and Full cover figures. The mismatch may disappear.
- If you want to match KDP's number, tick Override full cover width (use the size KDP asks for). A Full cover width (inches) box appears, with a note: enter the width from KDP's "expected cover size" message (the width must exceed twice the trim width plus bleed; for a 6 x 9 book that is 12.25 inches).
- Type the width. Quillen shows what that implies: for example, entering 13.2 gives "Spine becomes 0.950 inch, i.e. about 380 pages on this paper", and the panel updates to a spine of 0.950 inch, a full cover of 13.200 x 9.250 inches and 3960 x 2775 pixels.
- Compare the implied page count with your real one. If they are close, the override is a safe fix. If they are far apart, return to step 2 and find the real cause.
- Check the cover. The back, spine and front panels reposition to the new spine, and the checklist on the right warns you if text now crosses a fold or leaves the safe area.
- Click Export print PDF, upload it to KDP and check the previewer.
Checklist
- Noted the exact size KDP expects and the size of your file.
- Worked out the difference and converted it to pages.
- Checked trim size, paper type and page count against the uploaded interior.
- Fixed the input, or used the width override if the rest is right.
- Rechecked the implied page count is close to the real one.
- Re-exported, re-uploaded, and checked KDP's previewer.
- Ordered a printed proof.
Common questions
Why does KDP say my cover is the wrong size?
KDP calculates the expected cover size from your trim size, paper type and page count. Most mismatches come from the page count, which sets the spine width. Other causes are the wrong paper type, the wrong trim size or missing bleed.
How do I fix a cover that is too narrow or too wide?
Find the reason first: compare your cover's page count, paper and trim size with the interior you uploaded. Then correct the input and re-export, or set the full cover width to the size KDP asks for. In Quillen, tick Override full cover width and enter the quoted width.
How many pages is a 0.1 inch spine difference?
On cream paper (0.0025 inch per page) it is about 40 pages. On white paper (0.002252 inch per page) it is about 44 pages.
Is it safe to just match the size KDP quotes?
It is a quick fix, but check that the page count it implies is close to your real one. If it is far off, there is another problem such as the wrong trim size.
Do I need to redo my cover design after changing the spine?
The back, spine and front panels reposition, but check the preview: text can end up crossing a fold or leaving the safe area. Quillen's checklist warns about both.