Spine Width

What it does

• The spine is the only printed surface measured after the book exists.
• Text bulk plus two cover thicknesses plus a small allowance is the number.
• A spine built from the wrong caliper is a reprint, not a trim fix.

How to use it

1. Measure a printed signature with a micrometer rather than trusting the mill datasheet.
2. For perfect binding, add the cover thickness before rounding to 0.5 mm.
3. A spine that is 0.5 mm wide shows on a wrap cover as a cramped hinge.
4. Print the spine with a 3 mm bleed on each side and centre the text optically.

Safety notes

• Do not use page count alone; bulk depends on caliper and grain.
• If the cover is laminated, add the laminate thickness to both cover layers.