Why booklet page order looks wrong until you fold it

Take an eight-page booklet: two sheets of paper, folded together and stapled down the middle. Ask which pages are printed on the front of the outer sheet, and the answer is 8 and 1.

That is not a mistake. It is what folding does.

Working it out with one sheet of paper

Fold a sheet in half. You now have four faces: front-left, front-right, back-left, back-right. Number them as a reader would encounter them and you get page 4 on the front-left, page 1 on the front-right, page 2 on the back-left, page 3 on the back-right.

Add a second sheet inside the first and the outer sheet's numbers move outward — 8 and 1 on its front, 2 and 7 on its back — while the inner sheet takes 6 and 3, then 4 and 5.

The pattern: on every printed side, the two page numbers add up to one more than the total. For eight pages, every pair sums to nine. That single property is what makes a folded stack read in order, and it is the thing to check if imposition ever looks wrong.

Why it must be a multiple of four

Each sheet, folded, provides four pages. There is no way to produce a folded booklet whose page count is not divisible by four, so a nine-page document becomes twelve with three blanks.

Where those blanks go matters. Added at the end, they appear as blank pages at the back, which is what most people want. Added at the front, they push everything and produce a booklet that opens on an empty page. A tool that pads silently, without saying how many it added or where, is making a decision on your behalf that you may care about.

The gap at the fold

Text set close to the inner margin disappears into the crease, and on a thick booklet the inner sheets creep outward relative to the outer ones, so the effect is uneven through the stack.

A small gap at the fold — a few millimetres — costs almost nothing and prevents the most common complaint about home-printed booklets.

Printing it

Double-sided, flipped on the short edge. Long-edge flipping is the default in most drivers and it produces a booklet where alternate pages are upside down. If your first attempt comes out that way, this is invariably why.

Then fold the entire stack together, not sheet by sheet. Folding individually and assembling afterwards produces the pages in the wrong nesting order, which is a satisfying puzzle to diagnose and an annoying one to have printed forty copies of.

Before you impose

Unify the page sizes first. Imposition places two pages on a sheet by scaling them to fit, and pages of different sizes produce inconsistent margins across the booklet — visible immediately, and impossible to fix after printing.