Margin notes and annotated editions
Some books carry a second text beside the first. A study edition glosses a hard line. An annotated classic explains who the duke was. A textbook names the term the paragraph just used. A novel runs a second voice down the outside of the page, arguing with the narrator.
All of them depend on the same thing, and it is not a typographic effect. It is space. A marginal note needs a margin wide enough to hold it, and that margin is set when you choose the page, not when you reach the note.
The page decision comes first
An ordinary book page is nearly symmetrical: a modest outside margin, a slightly larger inside one to clear the binding. There is nowhere in it for a note to go.
A book with marginalia uses a deliberately asymmetrical page instead. The text block shifts toward the gutter and the outside margin opens up — commonly wide enough to hold a note two to four words to the line, plus a clear gap between the note column and the text it belongs to. That gap matters as much as the width: without it the note reads as a ragged second column of the same text.
You cannot retrofit this. Widening a margin changes the measure, the measure changes where every line breaks, and every page in the book falls differently. Decide it with the trim size, before the manuscript is poured. See Margins and gutters.
What the wide margin costs
Real numbers, on a 6 × 9 book. With a 0.5" inside margin — the working figure for a book up to 300 pages — and a 0.75" outside margin, the text measures 4.75" across. Open the outside margin to 1.75" to carry notes and the measure drops to 3.75". You have given away a fifth of every line.
Words per page fall roughly in step, so a manuscript that set to 300 pages now sets to about 380. That crosses a threshold: past 300 pages the inside margin should go to 0.625", which takes a little more width back off the measure.
The pages then reach the spine. On KDP white paper at 0.002252" per page, 80 extra pages thicken the spine by about 0.18"; on cream, at 0.0025", by 0.2". A thicker book costs more to print on every copy sold, for as long as it is in print.
None of that is an argument against marginalia. It is the bill, and you should accept it knowingly rather than discover it at upload. Changing your page count on purpose covers the levers if the total lands somewhere awkward.
In the Interior Formatter. It sets the inside margin from the real composed page count rather than an estimate, so the page you designed the note column into is the page you get — and the final count flows straight to the Cover Maker, where it sets the spine. Start your interior → · about the Interior Formatter
Setting the note
A marginal note is subordinate text and should look it. Set it smaller than the body — two or three points down is usual — and distinguish it further by italic, or by a contrasting face, most often a sans-serif against a serif body. One of those signals is enough; italic in a smaller contrasting face at a lighter weight is three, and the note starts shouting.
Align the note's first line to the line it annotates, not to the top of the paragraph. That alignment is the whole device: the reader's eye moves sideways, not up and down, hunting.
Set the note ragged on the edge away from the text block. Justifying a three-word measure produces word spaces you could park a car in.
And keep the notes short. The moment a note runs longer than the paragraph it hangs off, it has stopped being a gloss and started being a rival column, and the reader has to choose which book to read. At that length it is a footnote or a sidebar instead — see Footnotes, endnotes and the reader's patience and Sidebars, boxes and pull quotes.
The margin swaps sides
Left-hand and right-hand pages mirror, so the wide outside margin is on the left of a left-hand page and the right of a right-hand page. Your notes move with it. A note column locked to one side of the paper puts half the notes in the gutter, where the binding curve swallows them and the reader flattens the book with a thumb to read the text.
If a note has to sit near the gutter to make sense, the design has gone wrong somewhere earlier: the text block is in the wrong place, or the material is not marginal.
The annotated edition is a product
Annotating a public domain work is a real self-publishing niche, and it is one of the few where the layout is the thing being sold. The source text is free to anyone; your apparatus — the notes, the glosses, the context — is what a reader pays for, and it is your copyright even though the novel beside it is not.
That changes the standard the pages have to meet. The note column is not decoration on someone else's book; it is the book. Give it the same attention you would give body text, and be exact about what is yours on the copyright page. Reprinting a public domain book covers the rest of it.
In the ebook, margins do not exist
Reflowable text has no margin to write in. The reading system sets the measure from the screen and the reader's type size, and there is nowhere beside the text for anything to live.
So marginal notes become something else in the EPUB: an inline block after the paragraph, or a linked note the reader taps to open. Either one converts a glance into an interruption, which is a real change to how the book reads, not a formatting detail. Decide which notes survive that trip rather than converting all of them by default. Reflowable text, and the things that break it has the wider version of this problem.
Typeset your book
The Interior Formatter is free to use: name your book, bring your manuscript, and it sets real pages you can read before you commit to anything. You only pay when you want the files without the preview watermark.
Next: Citations and bibliographies in a printed book · Also in this guide: Margins and gutters · Bilingual books and facing-page layout · Reprinting a public domain book