How to print a booklet: the imposition rule, and the two settings that ruin it

Open the PDF in BOOKLET, which rearranges the pages, pads the count to a multiple of four with blanks placed where they belong, and can split a long document into signatures. Then print double-sided, flipping on the short edge, fold the stack and staple on the fold. The file is read and rewritten in the tab and is never uploaded.

The rule

A booklet is made of sheets folded in half. Each sheet therefore carries four pages: two on the front, two on the back. When the stack is folded together, the outermost sheet carries the first and last pages, the next sheet carries the second and second-to-last, and so on inwards.

Written formally, for a booklet of n pages, sheet i counting from zero carries:

front:   n - 1 - 2i   on the left,   2i       on the right
back:    2i + 1       on the left,   n - 2 - 2i on the right

For eight pages that gives:

Fold both sheets together and read from the front: 1, 2, 3, 4, 5, 6, 7, 8. It is worth doing this once with two sheets of scrap paper and a pen, because the order is genuinely counter-intuitive and nobody believes it until they have folded it themselves.

Why it is always a multiple of four

Because a folded sheet carries four pages and you cannot fold half a sheet. A nine-page document becomes a twelve-page booklet with three blanks.

Where those blanks go matters. Appending them to the end puts three blank pages at the back, which looks like a mistake. Placing them correctly — which the imposition rule does automatically, since the padded page numbers simply have nothing drawn on them — puts them where a printed booklet conventionally has blanks, typically the inside of the cover and the last leaf.

The two settings that ruin it

Flip on the short edge

This is the one that catches everybody. Double-sided printing has two modes, usually described as flipping on the long edge or the short edge, and they correspond to how a bound document turns: a portrait report turns on the long edge like a book, and a landscape document turns on the short edge like a flip-chart.

A booklet is printed on landscape sheets. Flip on the long edge and every second side comes out upside down relative to the one before it. The pages are in the right order and half of them are inverted, which is somehow more frustrating than getting the order wrong.

Print at 100%

“Fit to page” or “shrink oversized pages” scales everything down by a percent or two to allow for the printer's unprintable margin. On a booklet this shrinks each page slightly and, more visibly, moves the two pages on a sheet closer to the fold or further from it, so the gutter is wrong and the finished thing does not sit square.

Signatures, for anything long

A hundred-page document folded as a single booklet is twenty-five sheets folded together. The result has a spine that will not close, and it has a second problem: creep.

Creep is what happens because the inner sheets have to travel around the fold of all the sheets outside them. The innermost sheet sticks out further at the fore edge than the outermost one, by roughly the thickness of the paper times the number of sheets outside it. With twenty-five sheets of ordinary office paper that is several millimetres, so trimming the fore edge square removes several millimetres from the outer edge of the innermost pages — and if the text runs close to that edge, it removes text.

The answer, and the way real books are made, is to fold in signatures: groups of a few sheets folded separately and then stacked. Four or eight sheets per signature — sixteen or thirty-two pages — keeps creep down to a fraction of a millimetre and gives a spine that closes. Signatures are stacked in order, not nested, so page 33 begins the second signature.

Stapling on the fold

An ordinary desk stapler will not reach the centre of an A4 sheet. Three options, in ascending order of expense: a long-arm stapler, which is the proper tool and not expensive; opening a normal stapler flat, laying the sheet on a cork mat or a folded towel, driving the staple through and closing the legs by hand with a spoon; or folding first and stapling through the fold from the outside with the same trick.

Staple before trimming, not after, or the stack shifts while you cut.

The checks before you commit forty sheets

• Print the first sheet only, fold it, and confirm pages 1, 2 and the last two are where you expect.
• Confirm the flip: hold the folded sheet the right way up and check that the back is not inverted.
• Confirm the scale: measure something on the page you know the size of.
• Only then print the rest.

Three sheets of scrap paper answer all of that in two minutes, which is a great deal less than a ream and an afternoon.