Signature Calculator

Signatures — the folded, nested sections that get sewn together into a text block — come from folding a printed sheet in half repeatedly, and each additional fold doubles the pages it produces: this calculator uses pagesPerSheet = 2^(fold type) × 2, giving 4 pages for a folio (one fold), 8 for a quarto (two folds), 16 for an octavo (three folds), and 32 for a sextodecimo (four folds). If you nest multiple sheets inside one another before sewing (common with thinner paper, since a single fat signature sewn from one thick sheet holds together poorly), the tool multiplies pages-per-sheet by however many sheets you're nesting per signature to get the true pages-per-signature figure. From there it divides your total page count by that number and rounds up — you can't print a partial signature — which is why the tool also reports "actual pages," the true page count once every signature is filled, and flags any blank pages that had to be added to round out the last one.

It estimates each signature's thickness from paper weight using the rule of thumb that caliper (in mm) is roughly GSM × 0.00125, multiplies by sheets nested, then sums across all signatures for a rough finished text-block thickness — useful for sizing the spine before you cut cover boards. It also flags when a signature is likely too thick to fold and sew cleanly, using a tighter 2.0 mm ceiling for octavo and finer folds (where paper has already been folded three or four times and resists lying flat) versus 3.0 mm for folio and quarto. These are heuristics, not physical limits — actual paper behavior varies by fiber and finish, so test-fold a sample signature before committing a full run.