typesetting.ai

Book Margin & Gutter Calculator

Enter the trim size and page count to see the inside margin KDP requires and the actual text area left on the page.

Free · No sign-up · Nothing uploaded

Page count

Inside margin against the spine, on both pages

Inside (gutter) marginKDP minimum for this page count
0.5″
Outside marginKDP minimum is 0.25″, or 0.375″ if the book bleeds
0.5″
Top margin
0.75″
Bottom margin
0.75″
Text blockWhat's left for your words
5.00″ × 7.50″

At this trim KDP prints between 24 and 828 pages.

These are the numbers to type into your layout software. Or upload your .docx and we will apply them — including mirroring the inside margin across the spread, which is the part that is tedious to do by hand.

The requirement

KDP inside margin requirements by page count

These are minimums, not suggestions. A file under them is rejected at upload rather than flagged as a warning.

Page countMinimum inside margin
24–150 pages0.375″
151–300 pages0.5″
301–500 pages0.625″
501–700 pages0.75″
701–828 pages0.875″

The awkward part

The page count changes the gutter, and the gutter changes the page count

A wider inside margin narrows the text block. A narrower text block fits fewer words on a page. Fewer words per page means more pages, and more pages can push the book into the next band — which widens the gutter again.

  1. narrower text block
  2. more pages
  3. thicker book
  4. wider gutter

It settles after a pass or two, but only if something checks the finished length against the band it landed in. Near 150, 300, 500 or 700 pages it is worth checking twice — that is where a book measured once ends up with a margin one band too narrow.

Next

These are the numbers to type into layout software

If you are setting the book yourself, that is everything you need. If you would rather not, the print formatter applies the same geometry automatically — and measures the finished page count rather than estimating it, so the gutter matches the book you actually get.

Calculated the gutter?

Apply it automatically

Working out the cover?

Ready to format the interior?

Questions

Margins and gutters, answered

What is a gutter?

The inside margin — the one against the spine. It has to be wider than the outside margin because a bound book curves away from you near the binding, swallowing part of the page. The thicker the book, the more it swallows.

Why does the required margin change with page count?

Because the spine gets thicker. KDP publishes a table: 0.375″ up to 150 pages, then 0.5″, 0.625″, 0.75″ and 0.875″ as the book grows. These are requirements — a file under them is rejected at upload, not flagged as a suggestion.

There's a chicken-and-egg problem here, isn't there?

Yes, and it's real. A wider inside margin narrows the text block, which adds pages, which can push you into the next band and widen the margin again. That is why the calculator warns when you are close to a threshold. Our print formatter resolves it by rendering once to count pages, then re-rendering with the correct geometry.

Are the outside, top and bottom margins fixed?

No. KDP's floor for a no-bleed interior is 0.25″ on those three, but 0.25″ looks cramped in a finished book. The figures shown are what we use for a comfortable novel page: 0.5″ outside, 0.75″ top and bottom.

Do I need to add bleed?

Only if something is meant to run off the edge of the page — a full-bleed image or a coloured background. A text interior does not, and bleed changes the trim dimensions, so leave it off unless you know you need it.

Is this the same maths your formatter uses?

The same functions, literally — the calculator and the print formatter import from one module. If they disagreed, one of them would be wrong about a file you were about to send to a printer.

Checked against the source

The requirements on this page are published by the organisation below, not by us. We last read it in September 2026 and compared it against what the tool produces. If a requirement has changed since, the source is right and we are wrong — tell us and we will fix it.