Creep, and why the inner pages shrink

Creep, sometimes called shingling or push-out, is what happens when you nest several folded sheets inside each other. It affects saddle-stitched booklets and nothing else in this site’s list of bindings that matters much. It is a small effect, but it can cut text off the outer edge if you ignore it.

What actually happens

Paper has thickness. When a sheet is folded in half, the fold takes up a little room, and the sheet inside it has to wrap around that. Each sheet inside the nest sits on top of the ones outside it, so the innermost sheet is pushed out slightly further from the spine than the outermost.

After stapling, the printer trims the three open edges of the booklet flat in one cut. The outer sheets lose a small amount of paper at the fore-edge, and the inner sheets lose slightly more, because they stick out further. The visible result is that the margin of the inner pages is narrower than the margin of the outer pages. In an extreme case, text near the edge on the middle pages is cut.

How much

The shift per sheet depends on the paper thickness. A typical 80 gsm office paper is roughly a tenth of a millimetre thick, and heavier stock is thicker. These are approximate values, and different brands and finishes vary. For a nest of several sheets, the total shift for the innermost sheet is roughly the number of sheets outside it multiplied by the thickness of one sheet, with a small allowance for the fold itself.

That is the estimate used in the Folding Table. For 24 pages at 100 gsm, six sheets, the innermost sheet is pushed out by a bit more than half a millimetre. It is labelled an estimate on purpose. The real figure depends on the paper, the press, the folding machine and how tightly the stack is pressed before trimming.

When it matters

For booklets up to about sixteen pages on ordinary paper, creep is too small to see. A margin of 10 mm absorbs it without any change. For 24 to 40 pages on thicker paper it becomes visible: page numbers or running heads near the outer edge can look off, and any border drawn near the trim will be uneven.

It also matters for design choices. A thin line close to the page edge or a full-bleed picture is more exposed than text with generous margins, because the eye notices an uneven line more than an uneven white space.

Three ways to deal with it

1. Ignore it with generous margins. Keep at least 10 mm outside any text on the fore-edge. For short booklets this is all you need.
2. Let the print shop compensate. Many commercial printers and imposition programs adjust the position of each spread automatically, moving inner pages in towards the spine by a small step for each sheet. Ask them whether they do it. If they do, supply plain pages and do not compensate yourself, because applying it twice makes the margins uneven the other way.
3. Compensate in the file. If you impose the sheets yourself, shift each spread inwards by the estimated amount, with the outermost sheet at zero and the innermost at the full value. This takes software that can offset pages individually, and it is only worth doing for long runs or exacting layouts.

What the numbers in the table mean

The creep readout gives the total shift for the innermost sheet and the shift for each sheet in the nest. Use the total to judge whether your margins are safe. If the total is under half a millimetre, you can forget it. If it is over a millimetre, check your fore-edge margins and ask your printer.

Change the paper weight in the table and watch the figure change. Moving from 80 to 120 gsm roughly increases the shift by half, because the paper is thicker. Moving from sixteen to thirty-two pages doubles the number of sheets and increases the shift much more, because each extra sheet pushes the inner ones further.

Why not a perfect answer

Anyone offering a single exact figure for creep is simplifying. Paper compresses under the stapler, folds differ between machines, and a digital print on coated stock behaves differently from offset on uncoated. The table’s figure is a planning number. Treat it as a reason to keep margins generous, not as a measurement to the micron.

A test before the run

If you are printing more than a handful, make one dummy. Fold and staple blank sheets of the same stock in the same count, trim it the way the shop will, and measure the margin at the outer and inner pages. A few minutes with a ruler tells you more than any formula, and it costs nothing.