Separate body text from added pages
Use the body-text word count, then choose the trim and layout assumptions you intend to test. Font class is a model choice, not a selection of an installed typeface. Set margins that leave a positive text area; a larger page does not help if its margins use the extra space.
Enter image pages, front matter, and back matter separately. With body text present, the model also adds one page per chapter as an allowance. It does not predict actual chapter breaks or right-hand starts. With zero words, body pages and the chapter allowance are zero, but explicit added pages still count.
Compare plausible layouts using the range, not just its midpoint. Invalid counts or impossible text areas produce no estimate. A gutter warning asks you to review the margin assumption; it does not automatically change the layout. Run a new estimate after changing your assumptions.
The calculation uses local numeric inputs. You do not upload a manuscript or a font file.
What changes words per page?
| Layout choice | Effect in this model | What it cannot capture |
|---|---|---|
| Trim size | Changes the available page width and height | How the manuscript flows onto that page |
| Font class and point size | Change estimated character width and line capacity | The actual metrics of a particular typeface |
| Line spacing | Changes the estimated number of lines | Paragraph styles, headings, and local spacing overrides |
| Margins | Reduce the usable text area | Whether the final design places content correctly |
Usable width is trim width minus inside and outside margins; usable height is trim height minus top and bottom margins. The estimator combines that area with average character-width and word-length assumptions, then applies a density range. These are stack127 modeling choices, not a KDP pagination formula or a universal words-per-page rule.
The final range includes the entered additions and rounds each endpoint up to an even page count. It remains a planning range. The model does not choose paper or ink, so it cannot establish a universal maximum page count for the book.
Replace the estimate with the final PDF
Real typefaces, paragraph breaks, artwork, and chapter layouts determine the exported page count. Once the book is typeset, use that actual count to check its selected format against KDP's submission guidelines. Then use KDP's cover calculator for the final cover setup. An estimated count is not the final input for a production spine or an acceptance decision.