Why 100% print scale can still be wrong

“100%” can still be applied after an earlier stage has already changed the page. If the document was laid out for A4 and the dialog is set to Letter, or the printer driver silently fits content inside its unprintable margin, the browser's 100% value preserves the already-adjusted job. Match the document and physical paper sizes, turn off fit or shrink options in both dialogs, and verify a known ruler or grid after printing.

What to take away

Document size, selected paper and loaded paper must agree before a percentage scale has a physical meaning.
A printer's hardware margins can trigger a second fit-to-page operation outside the browser dialog.
Measure a known 50 or 100 mm feature; a visual page preview cannot prove physical scale.

The full explanation

A page can be laid out in real millimetres and still print at the wrong size, because the browser, the print dialog and the printer each get a chance to scale it. Getting graph paper or a calendar to come out at true size is mostly about knowing which settings to defeat. Read the complete guide for the reasoning, examples and definitions behind this answer.

Use the idea

Printable Graph Paper Plannerhow many 5mm squares fit on a sheet of a4 Printable Month Calendar Plannerhow many rows does a printed month calendar need Printable Ruled Paper Makerprintable lined paper maker

Sources

CSS Values and Units Module Level 4 — absolute lengthsWorld Wide Web Consortiumchecked Jul 31, 2026
ISO 216:2007 — Writing paper and certain classes of printed matter, trimmed sizesInternational Organization for Standardizationchecked Jul 31, 2026