Print finishing / Binding
Why a stapled booklet has to have a page count divisible by four
A booklet made by folding sheets and stapling through the spine, where every sheet carries four pages and the arithmetic is therefore not optional.
What is physically going on
Fold a sheet down the middle and you have created four pages: two on the front, two on the back. Stack several folded sheets inside each other, staple through the fold, and you have a booklet whose page count is necessarily a multiple of four. A twenty-two page document cannot be saddle stitched. It becomes a twenty-four page one, and the only question is where the two blank pages go and whether you chose their position or the printer did. That is the whole content of this constraint, and it is discovered late because a page count is not something a design review looks at.
The decisions
Reasons rather than a description of the code. Where a number depends on the stock or the press, the instruction is to get it from the printer rather than to quote one here, because spine width, creep and bulk are not constants.
- Round the page count up to a multiple of four at design time and decide where the blanks fall, rather than letting them land at the end by default.
- Put deliberate content on a page that would otherwise be blank if the document has anything that suits it: a notes page, a contact page, a back cover.
- Mark any genuinely blank page as intentionally blank if the document is formal, so a reader does not think a page failed to print.
- Remember the covers are part of the count. A four page cover section plus a twenty page inner section is twenty-four pages, not twenty.
- Keep the extent modest. Saddle stitch is for thin documents, and past a certain thickness the fold bulges and the creep becomes unmanageable.
- Never assume the printer will pad it sensibly. Padding is a design decision and they will make it for you if you do not.
What it means for the page rule
The page rule is the part of this a document author controls. The binder decides the gutter and the printer decides the creep allowance; the document's job is to leave the room those decisions need.
/* Saddle stitch: pages come in fours. Decide where the padding goes
rather than discovering it. */
@page blank {
size: A4;
margin: 30mm;
@top-center { content: ""; }
@bottom-left { content: ""; }
@bottom-right { content: ""; }
}
.intentionally-blank {
page: blank;
break-before: page;
height: 100%;
display: flex;
align-items: center;
justify-content: center;
color: #999;
font-size: 8pt;
letter-spacing: 0.12em;
text-transform: uppercase;
}
/* Rendered only when the count needs padding:
<section class="intentionally-blank">This page is intentionally blank</section>
Count the covers. Four cover pages plus twenty inner pages is
twenty-four, and twenty-two of anything cannot be saddle stitched. */What people do instead
Sending a document whose page count is not a multiple of four and letting the printer pad it. They will add the blanks at the end, which is usually the wrong place, and the first you know about it is a proof with two unexplained blank leaves before the back cover.
How to find out rather than assume
Count the pages in the rendered document, covers included, and divide by four. If it does not divide, the padding decision is still open and it is yours to make. Then fold a dummy at the real extent and see whether the fold sits flat.
Where this API sits in it
Outside it. This API renders HTML to PDF: it produces a sequence of pages at the size and margins your CSS and the render options set, and everything on this page happens afterwards, to paper, in a bindery. There is no imposition option, no binding option and no finishing option, and there could not be, because none of those are properties of a file. What the render does decide is the two things finishing cares about most: how many pages there are, and how much room is left at the edges. Both of those are set before anything is printed, which is why a finishing constraint discovered late is expensive and one designed for is free.
Frequently asked
Can the API impose the pages into printer spreads?
No, and you should not want it to. Imposition is done by the printer with tooling built for it, against the specific press, stock and folding scheme, and the input that tooling wants is single pages in reading order, which is what a render naturally produces. Supplying anything else means somebody has to undo it first.
How do I get the page count to a multiple of four?
By deciding where the padding goes rather than letting it land at the end. Add the blanks deliberately, style them with the blank page rule so they carry no folio or running header, and mark them as intentionally blank if the document is formal. Counting the covers into the total is the step people miss.
Do any of these apply to a document that is only ever read on screen?
No. This cluster is about physical operations on paper, so if a document is genuinely never printed, none of it is your problem. It is worth checking that assumption rather than making it: delivery notes, permits, method statements and invoices all end up on paper more often than the people generating them expect.
Related finishing topics
The operations that constrain each other, then the rest of the same group.
Creep in a folded booklet, and the margin that shrinks in the middle
The way inner sheets of a folded booklet push outwards past the outer ones, so trimming the stack flush takes more off the inner pages than the outer.
Supplying single pages, and letting the printer impose them
The rearrangement of pages into the order they have to be printed on a sheet, which is the printer's job and is made harder by supplying pages already paired.
Blank pages in a double-sided document, and making them deliberate
The empty sides that appear in any double-sided document, which are either chosen by you or produced by accident.
The inner margin a bound document needs and the outer one it does not
The extra width on the bound edge, which exists because a fastened document does not open flat and the innermost part of the page curves away from the reader.
Perfect binding, the spine width, and the page that will not open
Sheets glued at a flat spine rather than folded, which gives a printable spine and a document that opens less flat than a stapled one.
Back cover, as a layout problem
The block in the document that this constraint lands on.
Every finishing topic
The full list, grouped by binding, folding and trimming, and collation.
None of this is a render option, and none of it could be. What the render controls is that the page count and the margins are the ones the finishing needs.