Book margin and gutter calculator

The gutter is the inside margin, the edge of the page that goes into the binding. It has to be wider than the outside margin because part of the page disappears into the spine, and the thicker the book, the more it disappears. That is why KDP ties the inside margin to your page count.

An inside margin of 0.375 in for up to 150 pages, rising to 0.875 in for 701 to 828 pages. Top, bottom and outside margins must be at least 0.25 in without bleed and 0.375 in with bleed. These are minimums, and KDP rejects files that go below them.

KDP says that if your software has separate fields for the inside margin and the gutter, you should enter the same value in both. In Word, the simplest setup is Mirror margins with the inside margin set to the value above and the gutter left at 0, which gives the same inside space on every page.

They keep your text from being trimmed or lost in the binding, but a page set at the minimum can look cramped. Many print books use wider outside and bottom margins than the minimum. Treat these numbers as the floor, not the target.

On KDP, bleed raises the minimum top, bottom and outside margin from 0.25 in to 0.375 in, and your PDF page grows by 0.125 in in width and 0.25 in in height. The inside margin does not change. Choose bleed only when images or color reach the edge of a page.

They publish recommended margins, not KDP-style minimums. IngramSpark recommends at least 0.5 in on every side, plus a 0.125 in strip on the bind side for color books. Lulu asks for a 0.5 in safety margin and recommends adding a gutter as the page count grows. If you print with more than one printer, use the largest value for each margin.

KDP lists hardcover trim sizes on the same page as its margin table, and its hardcovers run from 75 to 550 pages, inside the ranges above. Hardcovers open less flat than paperbacks, so many designers add a little extra to the gutter.