Page numbers are settled long before a plate is imaged. They follow from the binding method, the page size of the book and the number of folds a printed sheet takes on its way to becoming a signature. Plan that arrangement badly and the press can run without a single fault while the bindery ends up with dropped leaves, drifting page positions or a book block that will not trim square.
Two Folding Routines: Work and Back, Work and Turn
Every signature starts as one sheet. How many page numbers that sheet carries depends on two things: how many times it is folded and whether the two sides are printed from separate plates or from the same plate turned over.
For a 16mo page size, a sheet printed work and back, with one plate for the front and another for the back, folds three times and carries 16 page numbers. The same 16mo format printed work and turn, where a single plate prints both sides and the sheet is turned over between passes, folds only twice and carries 8 page numbers. Move up to a 32mo page size and each count shifts by one fold: four folds work and back give 32 page numbers, three folds work and turn give 16.
Those figures are worth remembering, because they decide how a job is laid out before anything else is scheduled.
Start With the Binding Method
The first question in pagination is not how many pages the manuscript has, it is how the finished book will be held together. Saddle stitching, perfect binding, hardcover sewing, side stitching and thread sewing all impose different page arrangements on the same text.
A saddle stitched book nests all its leaves inside one another and drives two wire stitches through the fold at the spine. A perfect bound book collates folded signatures in reading order, glues them at the spine and trims three edges flat. A 16mo saddle stitched title and a 16mo perfect bound title of the same extent therefore cannot share a page plan. Decide the binding first, then number the pages to suit it.
From Page Count to Sheet Count
Work from the publisher's printing order. It states the total page count, and from that the sheet count follows by simple division. Take the page numbers a single sheet carries in the chosen format and folding routine, then divide the total page count by that figure. A 300 page book at 16 page numbers per sheet needs 18.75 sheets, which is the number the production department will actually buy paper against.
Paper Weight Limits the Number of Folds
Thin stock folds obligingly. At 32mo, paper of 60 gsm and below will take four folds on a sheet with no trouble. Above that weight the picture changes. Book paper and offset paper at 70 gsm and 80 gsm, and coated stock used for colour magazines, build a thick spine when folded four times. The folded edge becomes bulky, the trim allowance runs short and the page edges step in and out along the fore edge. Even when the folder forces the last fold through, the signature comes out misshapen and the finished book looks careless.
On heavier paper, cut the fold count. Fewer folds keep the signature slim, hold the page numbers and the type area in position and leave the bindery a clean edge to work with.
Where the Short Signature Goes
Publishers try to plan whole sheets, or a whole sheet plus a half sheet, because that is what printing and binding handle most cheaply. Real jobs rarely cooperate, and the last sheet often comes out at 0.75, 0.8 or 0.9 of a full sheet.
For perfect bound, adhesive bound and hardcover sewn books, keep the partial signature away from the back of the book. Set the short signature in front of the final complete signature instead. Pages glued at the spine hold; a thin signature stranded at the very end is the first thing to work loose, and loose leaves and dropped pages follow.
For saddle stitched books the advice reverses. A short signature or a few loose leaves belong near the middle of the book, well away from the fold where the wire stitches pass. Anything sitting at that fold gets pulled by the stitching and sooner or later tears out.
None of this takes long to check. Before a title goes to plate, confirm the binding method, confirm the format and folding routine, divide the extent by the page numbers per sheet, and match the fold count to the paper weight. Five minutes at the planning stage saves a reprint.