Guide
Book Sizes: Standard Trim Sizes Explained
The standard book sizes in inches and millimeters, which genres use which, what KDP and IngramSpark will print, and how the size you pick moves the page count and the printing cost. Every size comes from a printer or a published source, listed at the bottom.
By Corey Jackson, developer of Lacuna
Reviewed by Melissa Erin Jackson, author of 15 self-published books
Updated October 5, 2026 · Read about us
The short answer
The most common book size in the US is 6 x 9 inches (152 x 229 mm).1
- Thrillers, memoir, and self-help often run 5.25 x 8; non-fiction 5.5 x 8.5
- Children’s picture books: 8.5 x 8.5
- UK paperbacks: B-format, 129 x 198 mm
- 6 x 9 is the biggest common size KDP still prints at its regular page price (up to 6.12 x 9 in)
What a trim size is
The trim size is your printed book’s width and height, after the printer cuts it to size.7 It is written width first: a 6 x 9 book is 6 inches wide and 9 inches tall.
5.5 x 8.5 inches
5.5 x 8.5 in
140 x 216 mm
- On KDP
- Standard
- Used for
- General non-fiction; YA fantasy, sci-fi, and dystopian
- Next to 6 x 9
- 13% less page than a 6 x 9
- One page holds
- About 32 lines and 277 words at 11-point type
Trim, not paper
The pages are printed on larger sheets and trimmed down, so the trim size is the book you hold, not the sheet it was printed on. Every other measurement in a print file (margins, bleed, the cover) is set from it.
Trim versus bleed
Bleed is the extra 0.125 inches (3.2 mm) of artwork past the trim line that the cutter removes, so a background that runs to the edge never leaves a white sliver. Text pages do not need it; covers always do, and interiors with full-page images do.
Why it matters
The trim size sets the page count, and the page count sets the spine width, the printing cost, and the minimum price. Genres also settle on a few sizes; IngramSpark’s list of what established publishers choose is below.
Standard book sizes in the US
Inches first, because that is how US printers list them, with millimeters alongside, and where each size sits on KDP’s list.
| Size | Millimeters | On KDP | Used for |
|---|---|---|---|
| about 4.25 x 7 inMass-market paperback | 108 x 178 mm | Custom size | Pocket-size paperbacks, sold in airports, drugstores, and supermarkets as well as bookstores |
| 5 x 8 in | 127 x 203 mm | Small | Middle-grade fiction, inspirational and spiritual |
| 5.25 x 8 in | 133 x 203 mm | Small | Thrillers and mysteries, memoir, self-help, business |
| 5.5 x 8.5 in | 140 x 216 mm | Standard | General non-fiction; YA fantasy, sci-fi, and dystopian |
| 6 x 9 inUS trade (octavo) | 152 x 229 mm | Standard | General fiction, reference; the most common size in the US and KDP’s default |
| 7 x 10 in | 178 x 254 mm | Large | Reference |
| 8.5 x 8.5 in | 216 x 216 mm | Large | Children’s picture books |
Sources: IngramSpark, KDP, Wikipedia (“Book size”), Wikipedia (“Paperback”)
- 6 x 9 is “the most common trim size for books in the U.S.”, and KDP’s default.1
- IngramSpark puts general fiction at 6 x 9 and most other categories smaller: 5.5 x 8.5 for non-fiction, 5.25 x 8 for thrillers, memoir, and self-help.2
- Mass-market paperbacks started at 4.25 x 6.5 inches (Pocket Books, in the 1940s) and grew to 7 inches tall in the 1950s.4
- KDP has no preset for that size, but its custom sizes (4 to 8.5 inches wide, 6 to 11.69 tall) take it.1
IngramSpark’s most popular sizes by category
| Category | Trim size |
|---|---|
| General fiction | 6 x 9 in |
| General non-fiction | 5.5 x 8.5 in |
| Thrillers and mysteries | 5.25 x 8 in |
| YA fiction | 5 x 7 in |
| YA fantasy, sci-fi, and dystopian | 5.5 x 8.5 in |
| Self-help | 5.25 x 8 in |
| Memoir | 5.25 x 8 in |
| Middle-grade fiction | 5 x 8 in |
| Children’s picture books | 8.5 x 8.5 in |
| Reference | 6 x 9 and 7 x 10 in |
From IngramSpark’s “Picking a popular trim size for your book”, which reports what established publishers in each category are choosing.
UK and European book sizes
British trade sizes have names rather than numbers, and several of KDP’s odd-looking inch sizes are these in disguise.
| Name | Millimeters | Inches | On KDP |
|---|---|---|---|
| A-format | 111 x 178 mm | 4.37 x 7.01 in | Custom size |
| B-format | 129 x 198 mm | 5.08 x 7.8 in | 5.06 x 7.81 in |
| C-format | 135 x 216 mm | 5.31 x 8.5 in | Custom size |
| Demy | 138 x 216 mm | 5.43 x 8.5 in | Custom size |
| A5 | 148 x 210 mm | 5.83 x 8.27 in | 5.83 x 8.27 in |
| Royal | 156 x 234 mm | 6.14 x 9.21 in | 6.14 x 9.21 in |
| Crown Quarto | 189 x 246 mm | 7.44 x 9.69 in | 7.44 x 9.69 in |
| A4 | 210 x 297 mm | 8.27 x 11.69 in | 8.27 x 11.69 in |
Sources: Biddles, Wikipedia (“Book size”, C-format), KDP
What KDP and IngramSpark will print
The two print-on-demand printers most self-published books go through. Both take custom sizes inside a range; these are the presets.
Amazon KDP paperback trim sizes
| Group | Inches | Millimeters | Pages, black ink on white |
|---|---|---|---|
| Small | 5 x 8 in | 127 x 203 mm | 24 to 828 |
| Small | 5.06 x 7.81 in (B-format) | 129 x 198 mm | 24 to 828 |
| Small | 5.25 x 8 in | 133 x 203 mm | 24 to 828 |
| Standard | 5.5 x 8.5 in | 140 x 216 mm | 24 to 828 |
| Standard | 5.83 x 8.27 in (A5) | 148 x 210 mm | 24 to 828 |
| Standard | 6 x 9 in | 152 x 229 mm | 24 to 828 |
| Large | 6.14 x 9.21 in (Royal) | 156 x 234 mm | 24 to 828 |
| Large | 6.69 x 9.61 in | 170 x 244 mm | 24 to 828 |
| Large | 7 x 10 in | 178 x 254 mm | 24 to 828 |
| Large | 7.44 x 9.69 in (Crown Quarto) | 189 x 246 mm | 24 to 828 |
| Large | 7.5 x 9.25 in | 191 x 235 mm | 24 to 828 |
| Large | 8 x 10 in | 203 x 254 mm | 24 to 828 |
| Large | 8.25 x 6 in | 210 x 152 mm | 24 to 800 |
| Large | 8.25 x 8.25 in | 210 x 210 mm | 24 to 800 |
| Large | 8.5 x 8.5 in | 216 x 216 mm | 24 to 590 |
| Large | 8.5 x 11 in (US Letter) | 216 x 279 mm | 24 to 590 |
| Large | 8.27 x 11.69 in (A4) | 210 x 297 mm | 24 to 780 |
Source: KDP’s trim size page
- “Large” trim: wider than 6.12 inches or taller than 9 inches.1
- A large trim costs more per page: $0.017 instead of $0.012 for black ink on Amazon.com, so a 300-page book costs $6.10 to print instead of $4.60.8
- Custom sizes: 4 to 8.5 inches wide, 6 to 11.69 inches tall.1
- Hardcovers come in five sizes, from 5.5 x 8.5 to 8.25 x 11.7
IngramSpark
IngramSpark publishes ranges rather than a short list.
- Paperbacks on white paper: 4 x 6 to 8.5 x 11 inches.
- Paperbacks on crème or groundwood paper: up to 6.14 x 9.25.
- Hardcovers: from 5 x 8, up to 8.5 x 11 on white or 6.14 x 9.21 on crème.10
- Under 6.15 inches wide is “small”; wider costs more per page, whatever the height. So a 6.14 x 9.21 Royal is small at IngramSpark and large on KDP.11
How the size moves the page count and the cost
The same words fill fewer, bigger pages. Estimated printed pages at 11-point type with normal line spacing and the margins a paperback needs.
| Words | 5 x 8 in | 5.5 x 8.5 in | 6 x 9 in |
|---|---|---|---|
| 50,000 | 214 pages | 181 pages | 146 pages |
| 80,000 | 342 pages | 289 pages | 234 pages |
| 100,000 | 428 pages | 362 pages | 292 pages |
| 120,000 | 513 pages | 434 pages | 351 pages |
Page count
Going from 5.5 x 8.5 to 6 x 9 drops the page count by about a fifth. The words to pages calculator runs the estimate for any size, type size, and spacing.
Spine width
Fewer pages make a thinner spine: KDP’s white paper is 0.002252 inches a page, so 300 pages is a 0.68-inch spine and 234 pages is 0.53. The cover calculator gives the spine and the full cover size for your trim and page count.
Printing cost
KDP charges a fixed cost plus a per-page cost, so every page the size saves is money on every copy, and a large trim pays more per page. The royalty calculator shows the cost and royalty for any size on KDP, IngramSpark, and Lulu.
How to choose a book size
Five steps, in the order that saves rework. The size is the one decision you cannot undo cheaply once the book is formatted.
Start from the shelf your book will sit on
Measure three recently published books in your genre, or use IngramSpark’s list of what established publishers choose: 6 x 9 for general fiction, 5.5 x 8.5 for non-fiction, 5.25 x 8 for thrillers and memoir, 5 x 8 for middle grade, 8.5 x 8.5 for picture books. IngramSpark’s advice is to see what the major houses in your category are doing with their trim sizes.
Check that your printer offers it
KDP has sixteen US paperback presets plus A5, and custom sizes from 4 x 6 to 8.5 x 11.69 inches; IngramSpark takes paperbacks from 4 x 6 to 8.5 x 11 on white paper and up to 6.14 x 9.25 on crème. If you plan to print at both, choose a size both offer, and remember KDP’s large-trim price starts above 6.12 x 9 inches while IngramSpark’s starts at 6.15 inches wide.
Run the page count and the printing cost
Put your word count into the words-to-pages calculator for the two or three sizes you are weighing, then put each page count into the royalty calculator. An 80,000-word novel runs about 234 pages at 6 x 9 and 289 at 5.5 x 8.5, and at KDP’s $0.012 a page that is about $0.66 less to print, on every copy.
Decide on a hardcover now
KDP hardcovers come in five sizes: 5.5 x 8.5, 6 x 9, 6.14 x 9.21, 7 x 10, and 8.25 x 11 inches. If a hardcover is in your plans, pick a paperback size that is on that list too, so both editions share a trim size.
Format at that size and order a proof
Set the trim size in your formatting software before you adjust anything else, because the margins, gutter, headers, and cover all follow from it. Then order a printed proof. On KDP a proof costs the book’s printing cost plus shipping: $4.60 on Amazon.com for a 300-page 6 x 9 in black ink.
Try every size before you commit to one
Lacuna formats your manuscript at any KDP or IngramSpark size, in inches or millimeters, and shows the page count as you switch. Change the trim and every page reflows; the margins and bleed follow.
Click either screenshot to see it full size.
Import your Word document, pick one of 32 pre-made styles, and export a print-ready PDF and an EPUB from the same project, on Windows, Mac, and Linux. The trial is free with no time limit and every feature on; the one thing payment unlocks is generating the final files, so you can compare a 5.5 x 8.5 and a 6 x 9 page for page before you spend $149, one time.
What authors are saying
Real authors. Real books. Formatted with Lacuna.
I’m a cover designer and interior formatter by profession and run my own small publishing press, so trust me when I say I’m picky and my standards are high. InDesign has always been the only program that formats for print with the level of customization I need. For years, I’ve used it for print and another program entirely for ebooks to get the results I wanted. When I saw Lacuna, I immediately went to check it out and within an hour from having downloaded the trial, I was hooked.
This gives me so much more freedom with print options than other formatting programs like Atticus or Vellum while still making ebooks a breeze. The ability to work from one file and have separate print and ebook settings is a complete gamechanger. I’m still learning my way around the program and loving every second.
JJ Carpenter
The Haunting of Kenmore Asylum
I originally checked out Lacuna because somebody in a KDP publishing group I belong to asked if anyone had tried Lacuna out yet. I published nine other books using a different formatter, but I wasn’t happy with it. I ended up taking a look at Lacuna even though I was pretty much sold on Atticus or Vellum. Once I started diving into Lacuna and saw the ease of use and flexibility, I was absolutely floored. It was a no-brainer, and I purchased Lacuna. Since then the program has only improved. Corey is amazing at fixing things and streamlining processes.
If you take a look at the book that I formatted with Lacuna you will see, it would be pretty difficult to do something like that with one of those other formatting programs. Plus they cost more. In my opinion Lacuna is already the best formatter on the market and only getting better. Thanks, Corey and Melissa, for making this available.
NextGen Victory Press
3-Minute Wrestling Devotionals for Rising Athletes
I tried numerous formatting methods and followed endless instructions from publishing websites, but nothing ever turned out right. Since finding Lacuna, everything has changed. I’ve been able to update all my manuscripts effortlessly and give them the professional look they deserve.
Lacuna helped me perfect one of my most cherished stories, The Magic Globe, and finally present it exactly as I envisioned. It’s truly been a game changer for my author journey.
Samuel Graham Astley
The Magic Globe
Book size questions
What authors ask when they set up their first paperback.
Sources
- Paperback and hardcover print options, KDP: “the most common trim size for books in the U.S. is 6 x 9”, the default, the large trim definition, custom size limits, ink and paper locked after publishing. Checked 2026-10-05.
- Picking a popular trim size for your book, IngramSpark: popular sizes by category. Checked 2026-10-05.
- Book size, Wikipedia: US Trade is octavo (6 x 9 in); British A-, B-, and C-format; B-format and Penguin Classics. Checked 2026-10-05.
- Paperback, Wikipedia: Pocket Books’ 4.25 x 6.5 inch format and its 1950s growth to 7 inches; where mass-market paperbacks are sold; A-format is mass-market, C-format the largest UK paperback. Checked 2026-10-05.
- Standard book sizes info, Biddles, a UK book print manager: UK trim sizes in millimeters. Checked 2026-10-05.
- Paper size, Wikipedia: ISO 216 A4 (210 x 297 mm) and A5 (148 x 210 mm). Checked 2026-10-05.
- Set trim size, bleed, and margins, KDP: what a trim size is, the trim size list, page ranges, hardcover sizes, bleed. Checked 2026-10-05.
- Printing cost, KDP: $1.00 fixed plus $0.012 a page (regular) or $0.017 (large), black ink, Amazon.com. Checked 2026-10-05.
- How much do proof or author copies cost?, KDP: a proof costs the book’s printing cost. Checked 2026-10-05.
- Trim sizes, IngramSpark: paperback and hardcover size ranges by paper. Checked 2026-10-05.
- Rate card 2026, IngramSpark: “Small = <6.15 width”. Checked 2026-10-05.
- Word count for novels and children’s books: the definitive post, Writer’s Digest: picture books are “text for 32 pages”. Checked 2026-10-05.
See your book at every size
Download Lacuna free, import your manuscript, and flip between trim sizes with the page count in front of you. Pay $149 only when you are ready to export.
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