Last reviewed — 14 August 2026
For a straightforward text-led book, there is usually no commercial prize for choosing an unusual size. For an illustrated book, workbook, cookbook or gift book, however, the page design may legitimately drive the format decision.
What trim size means
The trim size is the finished width and height of the printed book after manufacturing. It is not the size of the Word document you happened to write in.
On KDP, common paperback choices include 5 × 8 in, 5.06 × 7.81 in, 5.25 × 8 in, 5.5 × 8.5 in and 6 × 9 in. KDP describes 6 × 9 in as its most common US paperback trim size. That does not mean every UK author should automatically choose it.
The decision I would make first
Ask these questions in order:
- What does the book need to contain? A text-only novel has very different layout needs from a cookbook full of photographs or a workbook with writing space.
- Where will it be printed? Check the current supported sizes for the printer or POD platform you will actually use before designing the interior.
- How many pages will the chosen size produce? A smaller page normally creates more pages, which can affect spine width, margins and printing cost.
- Does anything run to the edge of the page? If yes, you need to design for bleed.
- Does the book feel right as a physical object? Order a proof. Screen previews are useful, but they cannot tell you how the finished book feels in your hands.
Current KDP bleed rules
KDP says that if even one interior page needs bleed, the entire interior file should be set up for bleed and supplied as a print-ready PDF.
For a bleed interior, KDP requires artwork to extend 0.125 in (3.2 mm) beyond the top, bottom and outside trim edges. A 6 × 9 in book therefore uses a 6.125 × 9.25 in interior page size when bleed is included.
All KDP covers require bleed.
Current KDP minimum margins
KDP’s current minimum inside margin increases with page count:
| Page count | Minimum inside margin | Outside, no bleed | Outside, with bleed |
|---|---|---|---|
| 24–150 | 0.375 in / 9.6 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 151–300 | 0.5 in / 12.7 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 301–500 | 0.625 in / 15.9 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 501–700 | 0.75 in / 19.1 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
| 701–828 | 0.875 in / 22.3 mm | 0.25 in / 6.4 mm | 0.375 in / 9.6 mm |
These are minimum technical requirements, not a promise that the resulting page will look well designed. A professional formatter may deliberately use more generous margins where the typography and book type call for it.
What not to assume
A few rules of thumb get repeated online as though they were platform rules. They are not.
- A 300-page novel does not automatically need to move to 6 × 9 in.
- A non-standard trim size does not, by itself, prove that a UK wholesaler or bookshop will reject the title.
- KDP does not require a blanket 12–15 mm extra gutter for every 300-page book; its minimum inside margins are explicitly based on page-count bands.
- You should not use an old blog’s sample printing cost as today’s quote. KDP printing costs vary by marketplace, page count, ink, paper and trim category and can change.
Word setup for KDP
KDP’s own Word guidance is straightforward:
- Set the page size to the intended trim size first.
- Let Word recalculate the page count.
- Use mirrored margins.
- Set the inside and outside margins using the current KDP page-count requirements.
- If the interior needs bleed, increase the page dimensions accordingly and upload a PDF.
- Re-check the inside margin if editing changes the page count into a different band.
For complex books, Word can become cumbersome. InDesign, Affinity Publisher and specialist book-formatting tools give you more control. For simple novels and memoirs, Word can still produce a perfectly serviceable print interior when it is set up carefully.
Trim size by book type: sensible starting points
These are design starting points rather than mandatory UK standards:
| Book type | Sizes worth considering | Why |
|---|---|---|
| Novel / memoir | 5 × 8, 5.06 × 7.81, 5.5 × 8.5 in | Compact, familiar proportions for text-led books |
| General non-fiction | 5.5 × 8.5 or 6 × 9 in | More room for headings, tables and call-outs |
| Business / technical | 6 × 9 in or larger where needed | Useful when charts and structured content need space |
| Picture book | Choose around artwork and supported print sizes | The illustration format should drive the decision |
| Workbook / journal | Often 6 × 9 in or larger | Writing space can matter more than compactness |
Before committing, look at several successful physical books in your category and measure them. That is more useful than treating a generic internet table as a rule.
ISBNs and trim-size changes
Do not buy an extra ISBN simply because you have adjusted margins or corrected a production file. ISBN rules depend on whether you have created a distinct product or edition, not on a simplistic ‘changed the trim, buy another ISBN’ formula. Check the current guidance from your ISBN agency before making that decision.
VAT: one useful UK distinction
Qualifying printed books are zero-rated for UK VAT, and qualifying electronic publications have also been zero-rated since 1 May 2020. There are exceptions: products that are essentially stationery, for example unused diaries and some notebooks, can be standard-rated. If your product sits near that boundary, check HMRC’s current guidance rather than assuming that anything bound between covers is zero-rated.
When paying for formatting makes sense
DIY is sensible when the book is structurally simple and you are comfortable checking the technical details yourself. A done-for-you formatter becomes more useful when you have footnotes, tables, images, complex chapter styles, a picture book, a fixed-layout EPUB, or a KDP file that keeps failing review.
Publishing.co.uk’s current formatting options are on our book-formatting service page. Check that page for today’s scope and price rather than relying on an old article.
Final pre-upload checklist
- Confirm the selected trim size is supported by the platform and binding type.
- Recalculate page count after setting the final trim size.
- Check the inside margin against the current page-count band.
- Use the correct bleed dimensions if any interior element reaches the edge.
- Make sure important text and artwork remain inside safe margins.
- Recalculate the cover after the final interior page count is known.
- Upload and inspect the platform preview carefully.
- Order a physical proof before approving the book for sale.
Sources checked 14 August 2026
- Amazon KDP Help — Set Trim Size, Bleed, and Margins: https://kdp.amazon.com/en_US/help/topic/GVBQ3CMEQW3W2VL6
- Amazon KDP Help — Build Your Book: Format a Paperback Manuscript (Word for Windows): https://kdp.amazon.com/en_US/help/topic/G202145400
- Amazon KDP Help — Paperback Submission Guidelines: https://kdp.amazon.com/en_US/help/topic/G201857950
- HMRC / GOV.UK — Zero rating books and printed matter (VAT Notice 701/10): https://www.gov.uk/guidance/zero-rating-books-and-printed-matter-for-vat-notice-70110
