Paper & print sizes

Print and prepress dimensions: ISO A/B/C series lookup, bleed added to trim size for print-ready PDFs, book sheet and signature estimates from page count, and pixel dimensions to physical print size at a given DPI. Cross-link to photography print tools for camera-oriented workflows.

The ISO A series is built on a neat property: every size has the same aspect ratio, and halving the long edge gives the next size down, so A4 is exactly half of A3. That makes scaling between them lossless in proportion, unlike US Letter and Legal, which do not share a ratio. For anything going to a commercial printer, bleed is not optional — artwork that runs to the edge must extend a few millimetres past the trim line, because guillotine cutting has tolerance and a page trimmed slightly off will otherwise show a white sliver. Keep important text inside a safety margin for the same reason. Book signature estimates assume pages are printed in multiples determined by the press and folding scheme, which is why page counts usually round to a multiple of four, eight, or sixteen.