The five most used KDP trim sizes, plus A5 for the European market, and when each one is the right fit. Size is one of the first decisions when you format your book's interior.
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| Size | Measurements | Recommended use |
|---|---|---|
| 6 × 9 in | 15.24 × 22.86 cm | Non-fiction — the most used on KDP |
| 5.5 × 8.5 in | 13.97 × 21.59 cm | Fiction — the most popular for indie authors |
| 5 × 8 in | 12.7 × 20.32 cm | Compact fiction (romance, thriller) |
| 5.25 × 8 in | 13.34 × 20.32 cm | Fiction, roomier variant |
| 8.5 × 11 in | 21.59 × 27.94 cm | Workbooks, illustrated, coloring books |
| A5 | 14.8 × 21 cm | European standard |
Amazon KDP treats any size wider than 6.12 in or taller than 9 in as "large" (with a higher per-page cost) — worth keeping in mind before choosing a non-standard size.
The inner (gutter) margin isn't fixed: the more pages, the thicker the spine and the more inner margin the text needs so it isn't trapped in the binding. Gutter calculates it automatically from the book's final length.