Wrong trim or page size: fixing KDP's size error and Lulu's 'book size does not match

The trim size is the finished size of your book after it's cut, such as 6 x 9 inches or 5 x 8 inches. When you set up a print book, you pick one. The pages in your PDF must match that choice exactly, and every page must be the same size.

What the platforms say

KDP. Its help page on formatting issues has a section on choosing the wrong trim or page size. As at 4 October 2026, your PDF's pages must be exactly the trim you chose, or that size plus bleed (0.125 in wider and 0.25 in taller). KDP also wants single pages, not two-page spreads.

Lulu publishes its messages, so here they are word for word:

• "The book size you selected does not match the page size in the file you uploaded." This usually appears when you upload a replacement interior at a different size from the original. Resize the file to match, or start a new project at the new size.
• A message ending "does not match the book sizes Lulu offers" or "doesn't match the selected product type". Your page size isn't one of Lulu's trims. Resize to one that is.
• "The page size or orientation differs within your PDF." Some pages are a different size, or turned sideways. Lulu asks for every page to be the same size and the same way up (portrait or landscape).
• "We detected an error in your PDF." Lulu lists the problems underneath, and mixed page sizes is one of them.

IngramSpark asks for pages built to the exact trim size when there's no bleed, and won't accept spreads. Bookvault's upload check compares your PDF's page size with the book you've set up.

The usual causes

• Word's default page is Letter or A4, and it was never changed.
• The size was changed for one section but not the others. Word lets each section have its own page size.
• One page was turned to landscape for a map or table.
• A title page or illustration made in another program was added to the PDF at a different size.
• The trim chosen in the setup isn't the one the file was made for, or the trim was changed after the file was made.

How to fix it in Word

1. Go to Layout > Size > More Paper Sizes. Enter your trim's width and height (add bleed only if your book uses it). Under "Apply to", choose Whole document.
2. On the Margins tab of the same box, choose Portrait and again apply it to the whole document.
3. If you added pages from somewhere else, rebuild them in Word at the right size, or ask whoever made them for a version at your trim.
4. Save as PDF. Open the PDF and check its page size (in most PDF readers, File > Properties shows it). Scroll through to make sure nothing is sideways.
5. In your platform's setup, check the trim you chose matches the file.

A new page size moves your text around, so your page count will probably change. That can change your minimum margins and your cover's spine width, so check both. See fixing a cover that's the wrong size.

Using a designer, InDesign, Affinity or Canva? Set the document size to the trim (plus bleed if needed), make sure every page or artboard uses it, and export single pages, not spreads.

Check before you upload

Book trim sizes lists the trims each printer offers, so you can pick one that works everywhere you plan to print. Bervet's free spine width calculator also checks the page size of your interior and cover PDFs. The check runs in your browser and nothing is uploaded; checking a PDF needs a free Bervet account.