Perfect-bound and sewn books are printed in signatures: large sheets that are folded several times into a group of pages. A very common format is the 16-page signature: 8 pages on each side of the sheet, printed sheetwise (a separate plate for the front and the back), then folded three times.
The page order
For the first signature (pages 1–16), the front plate has two rows of four pages. The top row is printed upside down (shown in blue), so that heads meet in the middle of the sheet:
Front plate
Back plate
Notice that pages printed next to each other add up to 17 (4 + 13, 16 + 1, 5 + 12, 9 + 8), and each back page sits directly behind its partner: page 2 behind page 1, page 3 behind page 4. The next signature uses the same pattern with 16 added to every number.
Which sheet size?
| Book size | Common sheet | Note |
|---|---|---|
| A5 (148 × 210 mm) | A2 (594 × 420 mm) | Exact fit: pages are usually scaled to about 96% to leave a gripper |
| B5 (176 × 250 mm) | 70 × 50 cm | Four B5 pages are 704 mm wide, so a slight reduction (about 97%) is needed |
Because the book is trimmed on three sides after binding, a small reduction in page size is normal and usually invisible to the reader.
Collating marks
A small black block printed on the spine fold of each signature, stepping down a little for every signature. When the signatures are gathered in order, the marks form a neat diagonal line, so a missing or swapped signature is visible at a glance. They are ground off during perfect binding.
Blank pages
If the book isn't a multiple of 16 pages, the last signature is padded with blanks. A 293-page book becomes 19 signatures (304 pages) with 11 blank pages at the end.
Do it in seconds with ImpoGrid
Choose Book, open the PDF and pick your sheet. ImpoGrid detects A5, B5 or any page size, scales it to fit the exact sheet with your gripper, and builds every signature's front and back plate with collating marks. A 300-page book takes about two seconds, entirely on your computer.
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